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WxUSAF

January 29-30, 2019 Arctic FROPA

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2 minutes ago, Bob Chill said:

Fv3 another good run. It's running a lot colder that its brother from what i can tell on ncep. Makes me not trust either. 

Seems like temperature before the front, or how quickly heavy precipitation can cool boundary layer will be the real wild card. Not sure which way to lean, it may be different for all parts of our forum in terms of temps 

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5 minutes ago, wawarriors4 said:

Seems like temperature before the front, or how quickly heavy precipitation can cool boundary layer will be the real wild card. Not sure which way to lean, it may be different for all parts of our forum in terms of temps 

Yea, this one has been really tough to make a call on. We've been seeing a number of solutions that drop upwards of .50 qpf and the bulk of it is in a relatively short time. Only issue with temps is between the surface up to 2k'. Going to be a lot of thermometer watching tuesday. 

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4 minutes ago, NorthArlington101 said:

Surprised nobody shared these panels. This would be a nightmare travel scenario for DC.

096a71efb3278a6311f450960571312f.jpg

32e61f0489c3cee17cebfd7ae3bf7b8b.jpg

@GEOS5ftw

Shows what looks like 1" per hour rates too looking at the snow accums map from hours 45 to 48

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1 hour ago, showmethesnow said:

eurosnowfall.gif.f8f6d317f85b9bcc87634092c7bb818a.gif

 

eta: EPS Snowfall means were showing the snowfall maxes north and west of the cities but did not show the secondary max over the bay and eastern shore.

Didnt the models have a finger of heaviest snows extending SW from Eastern PA down into DC yesterday? Looks opposite now unless that secondary max is the finger and shifted E?

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Think it was mentioned yesterday on a bulletin but looking over things we could possibly get a sneaky and possibly intense little squall line mid day Wednesday through portions of the region as the Arctic cold front moves in. Will depend on what if any moisture is still available when it pushes through. Probably be some good mixing down of some higher wind gusts regardless.

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3 minutes ago, Ralph Wiggum said:

Didnt the models have a finger of heaviest snows extending SW from Eastern PA down into DC yesterday? Looks opposite now unless that secondary max is the finger and shifted E?

12zeurosnowfall.gif.2d4ba4e1caa0b5ec90e28909857d2d47.gif

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2 minutes ago, showmethesnow said:

12zeurosnowfall.gif.2d4ba4e1caa0b5ec90e28909857d2d47.gif

Overall the run doesn’t look that different to me, so not sure why the snowmap looks so different. Did it cut back QPF or is it because of temps?

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The latest from LWX:


.NEAR TERM /THROUGH TONIGHT/...

High clouds will be exiting the area later today giving way to
abundant sunshine with high pressure building over the area.

Clouds will start increasing again this evening ahead of next
low pressure moving through Michigan and its associated cold
front. Expecting light snow to break out after 07Z across far
west and nrn MD counties. Any accumulation through 12Z Tue will
be less than half inch.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...

Models have been indicating a secondary low pressure center
forming along the front as it moves across the area Tue
afternoon. Overall, guidance has trended wetter and colder
across the north with this system. Through midday Tue, expect
snow north of I-70 and west of Rt 15 with rain east and south of
there, then rain gradually changing to wet snow as colder air
filters in. Over the I-95 corridor, the changeover may not occur
until closer to sunset with a 3-6 hr period of moderate wet
snow falling at sfc temps likely around freezing before ending by
midnight Tue night. QPF is generally 0.1 to 0.5 inches with
highest amts along the I-95 corridor, but most of that would be
falling as rain or rain/snow mix. This translates to about 1-3
inches of snow with highest accumulations north of I-70.


Rapid clearing is expected Tue night after midnight, then Arctic
front will follow on Wed with rapdily falling temps during the
afternoon. Winds could gust up to 45 mph Wed creating dangerous
low wind chills. Snow showers or snow squalls may accompany the
front as it crosses the area or develop behind the front on the
strong NW flow.

 

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12 minutes ago, DCTeacherman said:

Overall the run doesn’t look that different to me, so not sure why the snowmap looks so different. Did it cut back QPF or is it because of temps?

Cut back a touch on the precip. Didn't really dive into the temps. Euro doesn't have the maps (at least that I can find) but going by the GFS the differences we are seeing with placement and amount of snow fall on the different models is probably due to how they are handling the intensity and the placement of the lift at both 850 and 700mb as they run through the region. The interaction between the two is important to get moisture into the colder air moving in. And the GFS has been somewhat erratic with those features. Probably should start focusing more on the Meso's at this point because the GFS will probably have a hard time nailing down those features. Wish I could find Euro maps for it because of its higher resolution as well.

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12 minutes ago, DCTeacherman said:

Overall the run doesn’t look that different to me, so not sure why the snowmap looks so different. Did it cut back QPF or is it because of temps?

Not much change in precip and thermals seemed like noise to me.  Razor thin here.

0269ACBC-17BA-48E3-B39E-A0E2E10DCAC8.png

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23 minutes ago, LP08 said:

Not much change in precip and thermals seemed like noise to me.  Razor thin here.

0269ACBC-17BA-48E3-B39E-A0E2E10DCAC8.png

Thanks for the map.  I guess it’s really gonna be all about the boundary layer.  Seems like most models agree on 0.25-0.5 QPF.  If we can get a quick flip we can score 3-5, if it’s 37 degrees with white rain at 00z wed we’re in trouble. 

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All the models are showing the precip max in eastern pa.  I am sad about that.  Why can't the blue be over me?

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54 minutes ago, DCTeacherman said:

Overall the run doesn’t look that different to me, so not sure why the snowmap looks so different. Did it cut back QPF or is it because of temps?

Qpf decreases about .1 but it was also temps were slightly warmer. Bad combo when it’s a marginal setup.  Can’t afford any bleeding when your on your deathbed already with marginal temps and modest qpf. 

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There's some convective instability in the mid-levels (~600-700 mb) at BWI on the GFS for Tuesday afternoon ahead of the first cold front; lapse rates in this layer are about 7C/km.

1066953275_Screenshotfrom2019-01-2806-42-16.thumb.png.cf41b5230d8d56c8eea536099036495c.png

Additionally, there is some moderate frontogenesis associated with the strengthening boundary just below this layer. This forcing in the convectively unstable region would allow for the some mid-level convection to be realized. The location of the unstable region is also within the dendritic growth layer, favoring more efficient ice crystal growth; isothermal temperatures near 0C below 850 mb would also support very large, wet aggregates. Of course, these temperatures may also turn out to be marginal for precipitation staying all snow.

gfs_temp_adv_fgen_850_neus_7.png

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1 hour ago, arlwx said:

The latest from LWX:


.NEAR TERM /THROUGH TONIGHT/...

High clouds will be exiting the area later today giving way to
abundant sunshine with high pressure building over the area.

Clouds will start increasing again this evening ahead of next
low pressure moving through Michigan and its associated cold
front. Expecting light snow to break out after 07Z across far
west and nrn MD counties. Any accumulation through 12Z Tue will
be less than half inch.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...

Models have been indicating a secondary low pressure center
forming along the front as it moves across the area Tue
afternoon. Overall, guidance has trended wetter and colder
across the north with this system. Through midday Tue, expect
snow north of I-70 and west of Rt 15 with rain east and south of
there, then rain gradually changing to wet snow as colder air
filters in. Over the I-95 corridor, the changeover may not occur
until closer to sunset with a 3-6 hr period of moderate wet
snow falling at sfc temps likely around freezing before ending by
midnight Tue night. QPF is generally 0.1 to 0.5 inches with
highest amts along the I-95 corridor, but most of that would be
falling as rain or rain/snow mix. This translates to about 1-3
inches of snow with highest accumulations north of I-70.


Rapid clearing is expected Tue night after midnight, then Arctic
front will follow on Wed with rapdily falling temps during the
afternoon. Winds could gust up to 45 mph Wed creating dangerous
low wind chills
. Snow showers or snow squalls may accompany the
front as it crosses the area or develop behind the front on the
strong NW flow.

 

Winds gusting to 45 Wednesday with temps ranging from single digits to low teens across much of the area by evening .Not very often does our area experience this combo and maybe we even hit the trifecta with snow squalls accompanying the artic front . A couple of the models have quite the temp gradiant north to south around noon on Wednesday before the crash which is interesting.  ...teens along the M/D line with low  30s DC south.  As far as tomorrow...I think it's coming down to a nowcast situation...should be fun.

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It’s hard to not invision this being a pretty simple frontal passage with rain turning to snow. An inch tops in the metro areas. 2 inches tops along the md/pa line. Two things that could provide a slight boom scenario would be 1) temps going in not being as high which would allow for an immediate change over. Or 2) some light snow early tomorrow morning as dipicted by some models that could be a surprise dusting .5” especially north and west. 

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3 minutes ago, MD Snow said:

It’s hard to not invision this being a pretty simple frontal passage with rain turning to snow. An inch tops in the metro areas. 2 inches tops along the md/pa line. Two things that could provide a slight boom scenario would be 1) temps going in not being as high which would allow for an immediate change over. Or 2) some light snow early tomorrow morning as dipicted by some models that could be a surprise dusting .5” especially north and west. 

Yeah.  Clicking through soundings on the 3k NAM showed around the DC area show the temps never getting below freezing until after precip pulls out.  I still think that if someone can get the .25 QPF over a 3 hour window, you can dynamically cool to <32 and accumulate, but I don't think that will be widespread and we will have lots of varying reports and conditions come tomorrow night.

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5 minutes ago, LP08 said:

Yeah.  Clicking through soundings on the 3k NAM showed around the DC area show the temps never getting below freezing until after precip pulls out.  I still think that if someone can get the .25 QPF over a 3 hour window, you can dynamically cool to <32 and accumulate, but I don't think that will be widespread and we will have lots of varying reports and conditions come tomorrow night.

The idea of just a simple, yet figorious frontal passage is becoming more likely especially as the meso’s come into range. Given their dispiction, it’s hard to see there being an extended period of heavy snow. Which is what you would need  Still could be a fun and dynamic event. I’m looking forward to it. This still has a chance to be one of the more wintery weeks of winter. Arctic front tomorrow, snow squalls on Wednesday, clipper on Friday, and deep cold Wednesday- Saturday. Sign me up! 

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1 hour ago, DCTeacherman said:

6z Euro cuts back again.  Now looks to be in line with other models with coating to 2 inches for most of the immediate DC area. 

Wondering if the outcome for tomorrow plays a hand in the potential snow squalls for Weds. PM. ? 

 

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44 minutes ago, MD Snow said:

It’s hard to not invision this being a pretty simple frontal passage with rain turning to snow. An inch tops in the metro areas. 2 inches tops along the md/pa line. Two things that could provide a slight boom scenario would be 1) temps going in not being as high which would allow for an immediate change over. Or 2) some light snow early tomorrow morning as dipicted by some models that could be a surprise dusting .5” especially north and west. 

The trough is going negative tilt with a lot of cross boundary flow and some pretty good forcing. This isn’t a typical front. 

But the waves impacts will be narrow. Somewhere is getting a 3-5” thump from this. But it could be north or northeast of us. That doesn’t mean it failed because it was a “typical front”. This is anything but. 

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2 minutes ago, psuhoffman said:

The trough is going negative tilt with a lot of cross boundary flow and some pretty good forcing. This isn’t a typical front. 

But the waves impacts will be narrow. Somewhere is getting a 3-5” thump from this. But it could be north or northeast of us. That doesn’t mean it failed because it was a “typical front”. This is anything but. 

But it isn’t as negative as it was 24hrs ago. What I mean by “typical” is surface depiction/precip field for our area.  It’s pretty vigorous otherwise. Most arctic fronts are.

12z NAM looks interesting for maybe some secondary development east of 95 tomorrow night. It also has a nice little slug of moisture up your way before the front goes through tomorrow morning. Would think maybe you could capitalize on that given your elevation? 

 

 

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NAM is developing the wave well northeast of us. The trend in the globals has been east for 48 hours now.  This was bullseying WV to central PA 3 days ago.  Hope the good looks yesterday weren’t just a temporary pit stop as the guidance continues to shift northeast. Not thrilled with how it’s heading. 

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