655 
fxus63 kdtx 220440 
afddtx 


Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan 
1240 am EDT Monday Mar 22 2010 




Aviation... 


Drier air that advected into the area earlier today will keep any 
low clouds associated with the storm system over the Tennessee 
Valley well south of the taf sites this morning. This storm system 
will lift across the upper Ohio Valley on today causing the 
northeasterly pressure gradient to increase. This increase along 
with increased daytime mixing will create some northeasterly gusts 
over 20 knots at times. Expect the gustiness in the winds to pick up 
shortly after sunrise. The edge of the deeper moisture is forecast 
to work back into the area through the day...resulting in a chance 
of MVFR ceilings and light rain late in the taf for the Detroit 
terminals and possibly fnt and ptk. 


&& 


Previous discussion...issued 955 PM EDT sun Mar 21 2010 


Update... 


Comparison of the 00z DTX sounding to the 00z apx sounding reveals 
the strength of the gradient in deep layer moisture over the 
region...with the apx sounding extremely dry /pw of 0.16 inch/. 
Regional radar and surface observation have been showing light rain on 
the back side of the deformation region associated with the storm 
system over the Tennessee/lower Mississippi valleys already 
spreading into far NE Indiana. With some weak middle level Theta-E 
advection forecast over extreme Southeast Michigan overnight and given the 
regional radar trends...will introduce a chance of light rain to 
locations along and southeast of an Adrian to downtown Detroit 
line. The only other update to the forecast will be to raise min 
temperatures a couple of degrees to account for the amount of high clouds 
and increasing northeasterly gradient overnight. 


Previous discussion...issued 323 PM EDT sun Mar 21 2010 


Short term...through tonight 


Quiet weather expected for the remainder of the afternoon and 
overnight. Middle-level cloud deck that was in place during the early 
part of the afternoon quickly thinned out as drier air infiltrated 
the region from the north. Additional cloud cover will try to work 
into the area from the south this evening and overnight in 
association with a low pressure system lifting towards the Ohio 
Valley. These clouds will struggle against dry air pushing down from 
the northeast...especially as depth and strength of dry 
northeasterly flow increases overnight. Have limited cloud cover 
tonight to mainly south of Detroit...with clear skies north of 
Flint. 12z apx radiosonde observation was extremely dry...and feel this is more 
representative of the airmass that will be in place tonight across 
the North County warning area. 


With regard to overnight precipitation chances...aside from drier 
air in place...NAM shows only very weak isentropic ascent after 06z 
and is no longer generating any quantitative precipitation forecast over the area. GFS remains an 
outlying wet solution in comparison to the NAM/Euro/RUC...and also 
kicks a suspicious looking shortwave up near the Michigan border by 
06z. Have therefore discounted the GFS solution and removed all 
mention of rain showers for the overnight period. 


Leaned heavily towards the cooler met numbers...and even a little 
below...for overnight mins given its better handling of the drier 
air. Lows tonight should range from the middle 20s to middle 30s...with a 
few locations from Flint northward even dropping into the low 20s. 


Long term...Monday through Sunday 


Large upper low tracking through the deep south will lift northeast 
into eastern Tennessee early Monday and spread moisture back north 
into the region. Even though this system will track well east of the 
area Monday/Monday night...it still appears that the western edge of 
the rainfall associated with the system will brush the southeast 
part of the County Warning Area...bringing a decent chance of light rain. Will make 
only minor adjustments to the forecast in this regard...basically 
delaying the timing of the precipitation until about noon or so. 


After this system lifts into eastern Canada...the area is basically 
left in between the southern/northern stream through Thursday or so 
with little/no precipitation and mild temperatures. 


This split flow pattern begins to break down Thursday into Friday as 
an aggressive northern stream shortwave dives from the Canadian 
prairies through the northern Great Lakes and into New England where 
it phases with another slow moving system ambling east through the 
central/southern Continental U.S.. while this will result in little/no rain or 
snow for the area as the phasing takes place so far east...it will 
lead to a cool down by late week as high temperatures return to the 
40s on Friday and remain at 50 or a bit below through the upcoming 
weekend. 


By the weekend...another significant trough will track east of the 
Mississippi Valley and models support at least a modest phasing 
between the northern/southern stream...and hence...a better chance 
at widespread precipitation across the area. Will include a chance 
of precipitation to end this long term forecast...but remain vague 
in any details given the usual uncertainty associated with day 7 
forecasting. 


Marine... 


High pressure will build over the northern Great Lakes into Tuesday. 
Meanwhile...a low pressure system will lift across the southern Ohio 
Valley late tonight and Monday...before tracking to the Atlantic 
coast on Tuesday. An increase in northeast winds is expected across 
all but the far northern portion of Lake Huron on Monday and Monday 
night as this system tracks east. The strongest winds are expected 
over the southern Great Lakes. Although wind gusts are expected 
to remain below Small Craft Advisory criteria...the long fetch over 
the length of Lake Erie should allow waves to build in excess of 4 
feet across the western Basin. A Small Craft Advisory is now in 
effect starting Monday morning for the Western Lake Erie nearshore 
zone. Additional small craft advisories for large waves may be 
needed by Monday night for the western shore of Lake Huron. The 
large waves should subside quickly on Tuesday as winds turn more to 
the north and begin to subside under a building ridge of high 
pressure. 


&& 


DTX watches/warnings/advisories... 
Michigan...none. 


Lake Huron... 
Small Craft Advisory...outer Saginaw Bay and the nearshore waters 
from Port Austin to Port Sanilac...from 8 PM Monday to 1 PM 
Tuesday. 


Lake St Clair...none. 
Michigan waters of Lake Erie... 
Small Craft Advisory...from 8 am Monday to 8 am Tuesday. 


&& 


$$ 


Aviation.....Kurimski 
update.......SC 
short term...hlo 
long term....dg 
marine.......hlo 




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