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Hoosier

April 27-28 Potentially Historic Super Late Season Winter Storm

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3 minutes ago, Baum said:

Given the rarity of a mid-late April accumulating snowfall I feel bad for LOT. They did not buy into the 4/14 event and got burned a bit. Would not be surprised that as they buy in this time things don't pan out the same way. Luck of the draw I guess. Either way, this last two weeks is for the "winters over" crowd that posts on December 26.

The northern tier seems pretty locked in for a warning criteria snowfall... or at least close enough to warning criteria.

Could make a solid argument to upgrade that tier below that is still currently in the watch.  Unfortunately for LOT it pretty much bisects the metro area, so the ramifications of handling it wrong would be magnified.  

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11 minutes ago, Hoosier said:

The northern tier seems pretty locked in for a warning criteria snowfall... or at least close enough to warning criteria.

Could make a solid argument to upgrade that tier below that is still currently in the watch.  Unfortunately for LOT it pretty much bisects the metro area, so the ramifications of handling it wrong would be magnified.  

A lot of proms and first communions this weekend. And i thought my kids got tough weather for those events.:o

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Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
905 PM CDT Fri Apr 26 2019

.UPDATE...
826 PM CDT

Main forecast update this evening was to upgrade the far northern
tier of counties along the WI/IL border to a Winter Storm Warning,
with confidence growing for mainly all snow and high totals for
these areas Saturday morning into Saturday evening. Have
maintained the Winter Storm Watch for the I-88 corridor in
northern IL, with lower confidence on rain/snow trends remaining.
Guidance still indicating a period of strong forcing is likely on
Saturday, associated with approaching mid/upper level trough and
surface low along with persistent and strong FGEN. While the area
may remain in a warmer air mass at the start of Saturday, guidance
pretty consistent with a colder pocket of air moving across
southern WI and northern IL during the morning.

Although boundary layer conditions may initially be on the warmer
side to offset snow, the arrival of this colder air and strong
forcing with dynamic cooling should help any rain moving across
far northern IL to transition over to a rain/snow mix by mid/late
morning, and then soon after all snow. Do think a cooler trend
with temps seems more probable for areas in the Warning in far
northern IL given the setup, and have trended the forecast this
way. This has provided a slightly quicker transition through
midday, with all snow then expected in the afternoon through the
evening. The arrival of steeper lapse rates and instability aloft
is still appearing likely in the afternoon, and have continued
slight chance thunder. This all will support a band of heavy wet
snow to fall in the afternoon, with hourly rates of 1-2 inches
still possible within the main band. Expect snow totals within the
warning to be around 5 to 8 inches. Snow may initially take some
time to accumulate on pavements, however, this heavy snow will
soon quickly overcome the warmer temps. Snow accumulating on the
pavements, greatly reduced visibility along with winds gusting to
around 40 mph will support hazardous travel Saturday afternoon.

Further to the south, along the I-88 corridor, confidence still
remains on the lower side with rain/snow trends. This lower
confidence includes where a likely very sharp snow gradient will
setup. Still tough to say how this system and precip trends will
evolve along this corridor, however, it`s possible that a
southward trend with this snow could continue. Nonetheless, with
this lower confidence, have continued the Winter Storm Watch for
this corridor. Further to the south, mainly rain is still
appearing likely with a chance of showers and thunderstorms in
the afternoon. The warm sector of this system is appearing to stay
south of the CWA on Saturday at this time, but it`s possible it
could clip locations south of the Kankakee river valley. If this
were to occur, will need to monitor the slight possibility for an
isolated stronger storm.

Rodriguez

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39 minutes ago, Baum said:

Either way, this last two weeks is for the "winters over" crowd that posts on December 26.

The winters over crowd always cracks me up. A 2 day thaw shows up on the models in January and you hear "Winter's over" from a few. It's always 100% incorrect. Once in a while they may luck out with a 2012 type year, but for the most part, the snow season in the lower Great Lakes lasts 6 months. It is not continuous, but  it's a long time between the first and last snow of the season so anything can happen. Speaking of time, here some food for thought. We are probably just 5.5 to 6 months away from the 1st snowflakes of the 2019-20 season:lol:

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Latest HRRR shifted north quite a bit, now in line with the 3k NAM.  Pretty much a lock now.  Should note that the HRRR has Cedar Rapids in a few hours of sleet before the backend snows hit.

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Looks like a burst of wet snow at the tail end of the event for this area.  Should exceed an inch of rain, with some thunder possible as well.  I'll be heading up towards Freeport/Stockton after work to get into the "good stuff".  Very interesting event to be sure, but it is a bit disappointing for this area to just miss out much like the system a few weekends ago.  

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Regarding LOT, here are my thoughts.

Gotta make the call with the overnight package on the counties in the current watch area.  Personally I think the preponderance of the evidence argues for a warning.  If not, then a beefy advisory at minimum with a very close eye on trends for possible upgrade to warning later this morning.

The tier to the south where nothing is currently in effect may end up needing an advisory, at least for the northern portions of those counties.  However, I'd be surprised to see them pull the trigger on that in the overnight package and there is more time to watch the trends for those counties.  

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26 minutes ago, Hoosier said:

00z Euro looks a little south, fwiw.  

But also, the low is a couple mb weaker and the snow amounts are down.

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6 minutes ago, hawkeye_wx said:

But also, the low is a couple mb weaker and the snow amounts are down.

Yeah

us_model-en-087-0_modez_2019042700_41_511_323.thumb.png.8437df789eb75e5109a9a97123731a89.png

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I was pleasantly surprised at how detailed the DTX forecast discussion was this morning. They lay everything out and the moral of the story is, very low confidence overall in what will happen here lol. They noted that being able to tap into more Lake superior air is going to increase wet bulbing in a portions of southern Wisconsin & northern Illinois, which is why there is higher snow impact there.  Right now they are calling for 1 to 2" of accumulation possible here with 2 to 4" possible in southeast Michigans higher elevations.

 

It's funny, Detroit averages 37 days per season with measurable snowfall and several dozen additional days with a trace. Snow falling is such a common occurrence in the Winter that you don't even notice flurries falling on a January day like you notice those first few flakes that flutter down in Fall. But it seems even worse now at the end of April. The mere possibility of measurable snowfall is causing quite a detailed analysis. Shows you how rare it is. The record snowfall for Apr 27 is a trace (2004) and Apr 28 is a trace (1977).

Issued at 443 AM EDT Sat Apr 27 2019

DISCUSSION...

A real pressure cooker type forecast for later today as a late
season, winter low pressure system is set to track through the
southern Great Lakes region. The consternation centers directly on
the critical thermal profile in the surface to 2000 ft agl layer
amidst what is expected to be a high rate of precipitation. The
temperature details of this environmental profile and timing of
subsequent cold advection in this layer will ultimately determine
the timing of precipitation type changes. There remains low forecast
certainty with regards to the amount of snowfall that will occur
this evening and tonight across Southeast Michigan.

Early today...Clear skies are in place over the majority of
Southeast Michigan with differential geopotential height rises and
narrow surface ridge axis influencing the state. The exception is
the northern Thumb northward through Lake Huron and northern Lower
Michigan where opaque stratocumulus deck is in place. Satellite
presentation suggests cold cyclonic flow the culprit with 875 mb
temperatures of less than 5C a good delineation for the cloud. The
cold low to midlevel air is forecasted to push to the south and east
in quick order which is expected to take the cloud out of the area.
No expectations of this cloud impacting Southeast Michigan. As a
result, expecting full insolation early today which will impact
temperatures. Warm Mos guidance was definitely noted and generally
raised the consensus forecast a degree or two for most of Southeast
Michigan. Highs today are expected top out around 50 degrees for
many areas.

Late afternoon...Steep, saturated isentropic ascent on the 315-319K
equivalent potential temperature surfaces will bring a strong wing
of warm air advection precipitation through portions of southern
Wisconsin and northern Illinois during the midday period, breaking
out over far SW Lower Michigan between 18-21Z. Precipitation will
begin to push into the cwa after 21Z as midlevel theta e ridge
spreads directly across the area. Near surface flow is forecasted to
remain light westerly which supports a fairly rapid onset to
precipitation once column saturation finally hits. There is some dry
air concerns in the lowest 6.0 kft agl, so kept PoPs at likely prior
to 00Z for areas south of I 69.

Early this evening...Survey of countless forecast soundings
concludes that precipitation will begin as rain for all areas.
Forcing for ascent will maximize lower in the column with main
frontal forcing in the 800-600mb layer. This change of the dominant
forcing will occur as the midlevel low pressure center favors the
direct differential cyclonic vorticity advection corridor over the
far southern cwa. Main takeaway from the sounding analysis is that
precipitation changeover relies on a subtle cold advection event in
the lowest 2000 ft agl sometime between 03-06Z. Thats where things
get a little interesting. Went hunting through the averaged
1000-900mb layer plan view progs and identified a couple of items. 1.
Light northwesterly flow will hold on over Southeast Michigan this
afternoon which will provide a land mass modified air mass to the
forecast area. The northern edge of this land modified air mass will
then become a pseudo cold front that will eventually open the door
to cold advection this evening as it is pushed southward. 2.
Upstream, the model data clearly shows an anticyclonically curved
flow trajectory over the cold waters of Lake Superior, down Lake
Michigan into portions of southern Wisconsin/northern Illinois. This
is a dramatically different source region to the underlying air mass
which will provide a much higher wet bulbing potential over WI/IL.
It is the orientation of these low level thermal gradients and
implied advections that then match up to WPC Probabilistic Winter
Precipitation Output that supports substantially higher probabilities
for high impact snow accumulations back to the west.

Forcing for precipitation will be outstanding this evening within
the aforementioned 800-600mb layer. Peak of the precipitation event
will occur in the 00-06Z time window with 700-500mb and 850-700mb
UVVs expected to reach 20 microbars per second. A great frontal
signature is noted in the soundings at 700mb with low static
stability above the front. Given the direct CVA, the potential
certainly exists for some isolated thunder, both with convective
rain or convective snow activity. High amount of column moisture
with 3.75 to 4.0 g/kg available to the lift. Given the ingredients
and high end frontal forcing, the potential exists for high snowfall
rates tonight once precipitation type changes over. Always easy in
these springtime systems to find large aggregation of snow crystals
which leads to 1 inch per hour rates or higher. As for total
snowfall amounts, limitations do exist with warm surface temperatures
this afternoon right up until the evening and the likelihood that a
bulk of qpf will fall in the form of rain. Probably the most
detrimental to snowfall amounts will be a warm and wet ground. This
will compromise crystal structure on the ground and hasten settling.
This definitely appears to be an event where those measuring hourly
overnight will see some impressive snow on elevated/grassy surface,
but those that wait until Sunday morning may feel underwhelmed. The
current forecast will read 2 to 4 inches possible in the higher
elevation of Oakland/Livingston/Macomb/Washtenaw Counties, with 1 to
2 inches both to the north and south of that corridor. Uncertainty
does exist with what impact the snow will have on area roadways. The
guess right now is slushy at daybreak. The most likely negative
impact of this event may very well be low visibilities in falling
snow late this evening and overnight.

There were two trends easily identified in the 27.00Z suite. 1. The
nam came in much higher with QPF. 2. The ECMWF was farther south
with the QPF and much tighter with the QPF axis over Southeast
Michigan. It is important to note the stark difference between the
NAM and ECMWF. Generally viewed the NAM as an outlier overall, but
did incorporate .75 to .80 inches liquid amounts for Lenawee and
Monroe Counties. Given all of the considerations, later timing of
precipitation changeover to snow, lower QPF trend through northern
Metro Detroit, potentially slushy roadways, very low WPC snowfall
probabilities, and a weekend nighttime event, the decision was made
to defer headline decisions to the dayshift.
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With Chicago in line to receive what appears to be a historic late-season 4"-8" snowfall (through the 6z guidance), the following are some statistics:

Biggest snowstorm April 25 or later:
3.3", April 25-26, 1910

Latest 4" or more:
6.8", April 15-17, 1961

Latest 6" or more:
6.8", April 15-17, 1961

Latest 8" or more:
9.1", April 5-6, 1938

4" or Greater (April 1 or later):
April 4, 1920: 6.4"
April 2-3, 1926: 6.1"
April 5-6, 1938: 9.1"
April 8, 1938: 4.5"
April 15-17, 1961: 6.8"
April 1-2, 1970: 10.7"
April 2-3, 1975: 9.8"
April 5, 1982: 9.4"
April 14, 2019: 5.4"

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34 minutes ago, donsutherland1 said:

With Chicago in line to receive what appears to be a historic late-season 4"-8" snowfall (through the 6z guidance), the following are some statistics:

Biggest snowstorm April 25 or later:
3.3", April 25-26, 1910

Latest 4" or more:
6.8", April 15-17, 1961

Latest 6" or more:
6.8", April 15-17, 1961

Latest 8" or more:
9.1", April 5-6, 1938

4" or Greater (April 1 or later):
April 4, 1920: 6.4"
April 2-3, 1926: 6.1"
April 5-6, 1938: 9.1"
April 8, 1938: 4.5"
April 15-17, 1961: 6.8"
April 1-2, 1970: 10.7"
April 2-3, 1975: 9.8"
April 5, 1982: 9.4"
April 14, 2019: 5.4"

I always like to compare stats to Chicago, though we will not see 4-8" in Detroit. Still, any measurable snow period would be only the 10th measurable snowfall this late, and 1"+ would only be the 5th time it has happened. If 0.2"+ falls, it will be the greatest snowfall this late in the season since 1923.

 

For Detroit (since 1880)

 

Biggest snowstorm April 25 or later:
6.0" - May 9, 1923

Latest 4" or more:
5.0" - May 21/22, 1883

Latest 6" or more:
6.0" - May 9, 1923

Latest 8" or more:
24.5" - April 6, 1886

4" or Greater (April 1 or later):

May 21/22, 1883: 5.0"

April 3, 1885: 4.0"

April 6, 1886: 24.5"

April 7, 1894: 6.0"

April 3/4, 1903: 4.9"

April 17, 1921: 4.5"

May 9, 1923: 6.0"

April 2/3, 1926: 5.6"

April 9/10, 1942: 4.2"

April 1/2, 1970: 4.2"

April 5/6, 1982: 7.4"

April 7, 2003: 4.9"

April 23/24, 2005: 4.3"

April 5/6, 2009: 7.2"
 

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10 hours ago, michsnowfreak said:

The winters over crowd always cracks me up. A 2 day thaw shows up on the models in January and you hear "Winter's over" from a few. It's always 100% incorrect. Once in a while they may luck out with a 2012 type year, but for the most part, the snow season in the lower Great Lakes lasts 6 months. It is not continuous, but  it's a long time between the first and last snow of the season so anything can happen. Speaking of time, here some food for thought. We are probably just 5.5 to 6 months away from the 1st snowflakes of the 2019-20 season:lol:

Even 2012 wasn't a wall-to-wall torch.

While March and May were very warm, April was "exceptionally normal" by Great Lakes standards (temp-wise).

 

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36 minutes ago, michsnowfreak said:

I always like to compare stats to Chicago, though we will not see 4-8" in Detroit. Still, any measurable snow period would be only the 10th measurable snowfall this late, and 1"+ would only be the 5th time it has happened. If 0.2"+ falls, it will be the greatest snowfall this late in the season since 1923.

 

For Detroit (since 1880)

 

Biggest snowstorm April 25 or later:
6.0" - May 9, 1923

Latest 4" or more:
5.0" - May 21/22, 1883

Latest 6" or more:
6.0" - May 9, 1923

Latest 8" or more:
24.5" - April 6, 1886

4" or Greater (April 1 or later):

May 21/22, 1883: 5.0"

April 3, 1885: 4.0"

April 6, 1886: 24.5"

April 7, 1894: 6.0"

April 3/4, 1903: 4.9"

April 17, 1921: 4.5"

May 9, 1923: 6.0"

April 2/3, 1926: 5.6"

April 9/10, 1942: 4.2"

April 1/2, 1970: 4.2"

April 5/6, 1982: 7.4"

April 7, 2003: 4.9"

April 23/24, 2005: 4.3"

April 5/6, 2009: 7.2"
 

Thanks for sharing this data. Hopefully, Detroit will pick up an inch or more.

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13 minutes ago, Powerball said:

Even 2012 wasn't a wall-to-wall torch.

While March and May were very warm, April was "exceptionally normal" by Great Lakes standards (temp-wise).

 

Wasn’t April cold, and it really screwed up a lot of crops? Apples specifically? I feel like I remember a very early leaf out which was then hit hard by April frost/freeze. 

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4 minutes ago, SchaumburgStormer said:

Wasn’t April cold, and it really screwed up a lot of crops? Apples specifically? I feel like I remember a very early leaf out which was then hit hard by April frost/freeze. 

It was a roller coaster month, which when it was all said and done (if I recall) averaged out to being less than a degree within the normal temp for April.

But yes, there were a couple hard freezes.

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3 minutes ago, SchaumburgStormer said:

Wasn’t April cold, and it really screwed up a lot of crops? Apples specifically? I feel like I remember a very early leaf out which was then hit hard by April frost/freeze. 

Yes 2012 was an agricultural disaster. There were frosts and freezes scattered throughout the month, including freezes at the end of April.  There were a few snow flurries a few times that April but nothing of consequence, at least here.  I remember in the fall of 2012, the price of local Apple cider was outrageous.  Thank goodness that year was a huge anomaly, and actually most Springs since then have had late leaf outs.

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45 minutes ago, Powerball said:

12z NAM is all rain for Detroit, which would be fine with me. 

Just curious, do you miss snow at all? I mean I would love to see snow tonight but it's the end of April so whatever happens happens. But going from a place where it snows often to a place where it almost never snows must be a shock to the system. 

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