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fxus63 kdtx 211105 
afddtx 


Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan 
705 am EDT sun Mar 21 2010 




Aviation... 


Last gasp of light precipitation will fade steadily during the first 
several hours of the forecast with no worse than lower VFR ceilings at 
times this morning. By midday...ceilings will lift to better than 10kft 
with solid VFR conditions for the rest of the forecast. Tonight will 
just see a thickening of this 6-10kt moisture from fnt south as low 
pressure over the deep south lifts northeast into Tennessee. 


&& 


Previous discussion...issued 318 am EDT sun Mar 21 2010 


Short term...today 


Today will be a salvageable portion of the weekend with temperatures 
running close to normal and a steadily decreasing potential for 
precipitation. Dry conditions this afternoon will help readings warm 
into the upper 40s as the recent shallow supply of cold air is 
readily modified. The Tri Cities and thumb will have some afternoon 
sun filtered through high clouds which will be needed to battle the 
cooling effect of NE winds off of Lake Huron. 


Once precipitation finally began from Pontiac southward, the 
relatively warm air above the shallow front was revealed in a mix of 
rain, snow, and snow pellets. This is actually in good agreement 
with the DTX 00z sounding that showed a near freezing layer around 
800 mb and supports model soundings and critical thicknesses that 
are even warmer to the south. The good news is that any additional 
precipitation will be light and temperatures will settle right 
around the freezing mark before warming above shortly after sunrise. 
The light precipitation, relatively warm ground, and temperatures 
bouncing off the freezing mark will help avoid any problems due to 
the wintry mix. 


The latest model data continues to advertise a weakening of this 
frontal system during the morning, judging from Theta-E cross 
sections and departure of the entrance region of the upper jet. 
Modest instability rooted closer to the surface front over Ohio and 
Indiana has proven sufficient to support showery precipitation early 
this morning despite the weakening frontal circulation. Therefore, 
still expect at least scattered rain/snow showers over about the 
south half of the area during the morning with just a chance of 
light freezing rain mentioned early. The potential for additional 
precipitation will then become quite restricted by afternoon due to 
confluent flow aloft downstream of the short wave ridge associated 
with the large low pressure system to our south. 


Long term... 


Unusually deep upper level low moving through the western Gulf 
Coast states...as 500 mb heights are a good 4+ negative 
standardized anomaly. Latest trends of the 
GFS/NAM/Canadian/UKMET/European show the northern fringe of this 
system impacting southeastern areas of the County Warning Area Monday-Monday night 
as the system lifts northeast. Deformation zone does impact 
Southeast Michigan with the 850-700 mb Theta-E ridge axis 
sharpening up. Will ramp up probability of precipitation for the south half/east. The good 
news is there should be no precipitating type concerns...as 850 mb 
temperatures prognosticated to be greater than +3 c. 


Height rises on Tuesday will be a bit more tempered...as the upper 
level ridge is now forecasted to be a bit flatter...with eastern 
areas likely dealing with some morning clouds with the departing 
storm system. In any event...middle 50s for highs still appear do-able. 


Shortwaves/energy rolling into the Pacific northwest will track 
through the northern Continental U.S....with shortwave trough already 
forecasted to swing into the western Great Lakes Tuesday night. 
Pretty good low level cold advection prognosticated during Wednesday...as 
850 mb temperatures drop below zero by day's end (per 00z European and 
gfs)...and have adjusted maxes down a bit...near 50 north to middle 50s 
south. 


Much stronger northern stream trough (extension of polar vortex 
sliding over Hudson bay) then forecasted to swing through the 
northern Great Lakes on Thursday. The 00z GFS showing respectable 
height falls extending into the southern Great Lakes. However...very 
little moisture to work with...and from a surface pressure 
perspective...the cold front is not well defined...and will maintain 
the dry forecast. 


Marine... 


High pressure will build over the northern Great Lakes today and 
hold through Monday as a low pressure system moves through the 
central Appalachians. This will bring improved wind conditions over 
Northern Lake Huron but will result in a renewed surge of northeast 
winds by Monday toward the south end of Lake Huron and points south 
through Lake St Clair and Western Lake Erie. There is some potential 
for waves to reach Small Craft Advisory criteria due to the 
northerly/onshore direction but gusts will likely stay below 25 
knots through Tuesday. The low pressure system is then expected to 
move far enough east to allow high pressure to settle move overhead 
by Tuesday night. 


&& 


DTX watches/warnings/advisories... 
Michigan...none. 
Lake Huron...none. 
Lake St Clair...none. 
Michigan waters of Lake Erie...none. 


&& 


$$ 


Aviation.....Dg 
short term...bt 
long term....sf 
marine.......bt 




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