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fxus63 kdtx 161920 
afddtx 


Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan 
320 PM EDT Tuesday Mar 16 2010 


Short term...tonight 


Surface ridging (extending from the large dome of high pressure over 
the northern plains) will hold over lower Michigan through tonight. 
Deep layer of dry air in place...evident by 12z DTX and apx 
radiosonde observations...will continue to allow for a large diurnal swing in 
temperatures. After reaching highs near 60 this afternoon under 
nearly full-insolation for middle March...will see lows fall close to 
the previous night in the middle 20s to low 30s. Went several degrees 
below MOS for our typical good radiating areas such as Flint and Bad 
Axe...where MOS has been performing poorly. 


&& 


Long term... 


Beautiful stretch of weather to continue during the next couple 
of days...but the forecast GOES downhill for the weekend. 


Very dry airmass in place over lower Michigan...as 12z apx sounding 
came in with a precipitable water value of 0.09 inches. This dry air sets the stage 
for large diurnal swings (30 degrees)...as witnessed today. Based on 
the readings today and yesterday compared to guidance...and 
factoring in better mixing...warmer 850 mb temperatures...and low level 
winds shifting around to a more favorable westerly 
direction...planning on carrying lower 60s Wednesday...with middle 60s 
expected on Thursday ahead of the moisture starved cold front...as 
850 mb temperatures rise to around 5 c. With some middle/high clouds around 
on Friday...and low level cold advection bleeding into Southern 
Lower Michigan...looking at a south to north temperature 
gradient...and will tighten up the maxes a bit...lower 50s north to 
lower 60s south near the Ohio border. 


Still looking for a storm system to impact the region over the 
weekend...as model consensus is for a longwave trough to develop 
over the eastern half of North America by Monday. It looks like 
phasing of the two branches will occur a bit too late for US...with 
mostly a rain event as the southern wave comes out of The Four 
Corners and the mild western Gulf moisture streams northward. The 
model trends over the past two cycles support a delayed arrival. 
However...it is possible we could see two waves of low pressure ride 
along the boundary...a weak one Saturday...with the stronger one on 
Sunday. Have gone ahead and upped probability of precipitation to likely on Sunday. But 
again...regardless of the solution...12z 
GFS/Canadian/European...just too warm during the daytime hours to 
support snow with the track through or just west of the County Warning Area. The 
northern stream wave/trough and cold air should then swoop in for 
Sunday night...allowing for a changeover...with Monday looking to be 
the coldest day of the week...as 850 mb temperatures fall to at least -10 
c...which supports holding maxes in the 30s. Until the system fully 
comes ashore...adjustments with the timing of the phasing and track 
of the low remain possible. 


The upper level trough axis already reaches the East Coast by 
Tuesday morning...with good height rises and low level warm 
advection ensuing over the Great Lakes region...supporting 
temperatures modifying a bit...but still below normal on Tuesday. 


&& 


Marine... 


A strong and expansive dome of high pressure centered over the 
northern plains will slowly drop southeast through Thursday. Ridging 
from this system will extend into the central Great 
Lakes...maintaining light winds and mostly clear skies. A weak low 
pressure system will drop across central Ontario late Thursday into 
Friday...bringing an increase in westerly winds. 


&& 


Previous discussion...issued 126 PM EDT Tuesday Mar 16 2010 


Aviation... 
a deep layer of dry air will allow VFR conditions to prevail 
throughout the taf period. Turbulent mixing into northeast winds 
aloft this afternoon will allow surface winds to also turn 
northeast...with speeds from 4-7 knots. Winds will become light 
and variable around sunset as we lose daytime heating. 


&& 


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


&& 


$$ 


Short term...hlo 
long term....sf 
marine.......hlo 
aviation.....Hlo 




You can obtain your latest National Weather Service forecasts online 
at www.Weather.Gov/Detroit (all lower case).