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September 2016 General Discussion


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AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
1048 AM CDT TUE SEP 6 2016  
   
UPDATE  
  
1030 AM CDT  
  
NO SIGNIFICANT CHANGES TO THE FORECAST AT THIS POINT, HOWEVER,  
TEMP AND DEWPOINT TRENDS ARE A LITTLE CONCERNING GOING INTO MIDDAY  
AND THE AFTERNOON. LATEST OBSERVATIONS ARE SHOWING MID TO UPPER  
70S DEWPOINTS PUSHING INTO THE CWA AND WITH CURRENT FORECAST HIGHS  
OF AROUND 90 DEGREES, WOULD PUT HEAT INDICES IN THE 100 TO 105  
RANGE FOR MOST LOCATIONS WITHIN THE CWA. LOCATIONS OVER THE  
SOUTHERN CWA, MAINLY SOUTH OF I80, WILL LIKELY OBSERVE THE HEAT  
INDICES CLOSER TO 105. AT THE TIME, EXPECTED HEAT INDICES WOULD  
NOT SUPPORT ANY HEADLINE. AM CONCERNED THAT TEMPS COULD RISE A  
LITTLE HIGHER THAN FORECAST, AND COULD PUT HEAT INDICES MORE  
AROUND 105 FOR A TIME THIS AFTERNOON. MAY GO AHEAD AND ISSUE AN  
SPS TO HIGHLIGHT THIS POTENTIAL MORE TODAY, AND WILL CONTINUE TO  
MONITOR TRENDS.  
  
DID NOT ADJUST POPS THIS MORNING THINKING THAT THE BULK OF ANY  
PRECIP ACTIVITY WILL STAY JUST OUTSIDE OF THE CWA. HOWEVER, SHORT  
TERM GUIDANCE IS SHOWING SOME ISOLATED CONVECTION ACROSS THE FAR  
SOUTH/SOUTHEAST CWA THIS AFTERNOON. GIVEN THE HIGH DEWPOINT AIR  
AND DIURNAL HEATING SUPPORTING INCREASING INSTABILITY IN THIS  
LOCATION, THIS DEFINITELY SEEMS REASONABLE. LACK OF ANY REAL FOCUS  
AND LARGE SCALE ASCENT ALONG WITH WARMER TEMPS ALOFT SHOULD LIMIT  
COVERAGE AND INTENSITY THIS AFTERNOON THOUGH.  
  
RODRIGUEZ  

 

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30 minutes ago, Chambana said:

Those dp readings in Pontiac always seem suspect, multiple occasions in the summer where they record 81-82 readings meanwhile everyone else is in the 76-78 range. 

 

 

Yeah they tend to run a bit higher.  I'm not sure what the particular setup is there.  May not necessarily be a flawed instrument but positioning too close to a field of crops.  

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Looks like a nice reprieve from the high humidity arrives by early Saturday for all of us.  Sub 60 dews Sat through Mon.  A little tentacle of higher dews spikes up around next Tue, but it looks fleeting.  I think after this week we're done with these multi-day 70+ degree dew days.  The way this year is going though, who knows lol.

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Looks like a nice reprieve from the high humidity arrives by early Saturday for all of us.  Sub 60 dews Sat through Mon.  A little tentacle of higher dews spikes up around next Tue, but it looks fleeting.  I think after this week we're done with these multi-day 70+ degree dew days.  The way this year is going though, who knows lol.

This morning's GFS and Euro are showing the first big chill diving south from Canada mid next week.  The GFS actually has a freeze down to near La Crosse, with upper 30s down into eastern Iowa, and highs only in the mid 60s.  That'll be quite a change if it holds.  

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This morning's GFS and Euro are showing the first big chill diving south from Canada mid next week.  The GFS actually has a freeze down to near La Crosse, with upper 30s down into eastern Iowa, and highs only in the mid 60s.  That'll be quite a change if it holds.  

 

That will be nice.  As warm as it is out there today it's hard to believe we are now <3 weeks away from the earliest snowflakes to have fallen in this area on record.  September 25 1942.  

Looks like 92 will end up being our high for today.  Dews have mixed back a bit.  Down to 73 after hovering in the 75-76 degree range much of the day.

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This morning's GFS and Euro are showing the first big chill diving south from Canada mid next week.  The GFS actually has a freeze down to near La Crosse, with upper 30s down into eastern Iowa, and highs only in the mid 60s.  That'll be quite a change if it holds.  

GFS is always ultra aggressive with early cold snaps, I will take the over on all of that.

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GRR delivering the goods...:scooter:

[quote]000
FXUS63 KGRR 061927
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
327 PM EDT TUE SEP 6 2016 

We believe there is a threat for flooding early Wednesday night
along with a potential tornado environment reminiscent of August
20th. A 40+ knot WSW low level jet... anomalously strong for this
time of year...is expected to develop and transport enough
moisture to boost precipitable water (PWAT) values to over 2
inches. Propagation effects from the low-level jet will offset
movement driven by mean winds in the cloud bearing layer, setting
the stage for training storms.

Low LCL heights and a warm mid-troposphere will provide a very deep warm cloud layer conducive to efficient collision-coalescence rain processes. Locally large rainfall rates/amounts will therefore be possible, particularly with training storms.

This environment also enables convective instability to concentrate down low //evidenced by forecast 0-3km MLCAPE around 100 J per kg// which could then stretch vorticity associated with low-level shear //0-1km bulk values of 20-30 kts// in the vicinity of the low-level jet. This is where the concern for short-lived tornadoes lies.

The scenario described above may fail to materialize if outflow from large multicell clusters dominates the overall environment. However...a tornado threat will remain possible with any relatively isolated convective segments that develop. The key factor will be watching surface observations to see if winds remain consistently backed to the south or southeast without being overrun by outflow. This was a key indicator on the 20th and could again be important early Wednesday night.[/quote]

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Also, this nugget from DTX...:sun:

000
FXUS63 KDTX 061912 CCA
AFDDTX

Area Forecast Discussion...corrected typo
National Weather Service Detroit/Pontiac MI
306 PM EDT TUE SEP 6 2016

Tomorrow remains challenging forecast as ridge still looks to be
holding up fairly well, as heights remain at or above 588 DAM, with
700 mb temps aoa 10 C. None-the-less, MLcapes on the order of 1000-
2000 J/kg with weakening to NIL Cap during the afternoon, and with
very moist airmass (PW values above 2 inches), will only takes a few
cells to get going with renewed activity on any outflow boundaries,
as highs are expected to be around 90 degrees again. With the
isolated activity generated this afternoon, felt compelled to
increase pops a little bit tomorrow (20 south to 55 near Saginaw
Bay), as there is surface trough/warm front noted in 12z euro
lifting through southeast michigan toward 00z Thursday. If night
shift has increased confidence in activity not materializing across
southern half of the cwa, may need heat advisory for Detroit Metro
Area as heat indices push toward 100 degrees once again.
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Not having a substantial breeze really does make a difference as you guys said.  Was just outside and the air feels heavier than before.

I actually wasn't all that breezy IMO, other than the typical Florida-like surface vorticity stirred up from the low-level CAPE. 

Both DTW and DET officially made it to 91*F today.

I also forgot to mention that it had rained where I worked this morning (which was completely unexpected). 

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I actually wasn't all that breezy IMO, other than the typical Florida-like surface vorticity stirred up from the low-level CAPE. 

Both DTW and DET officially made it to 91*F today.

I also forgot to mention that it had rained where I worked this morning (which was completely unexpected). 

Was pretty breezy over this area today.  20-25mph winds much of the afternoon.  Looks like a repeat tomorrow regarding the winds.

Dews mixed into the low 70s later in the afternoon, and never bumped back up after that.  

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