Weather

349 
fxus63 kdtx 060830 
afddtx 


Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan 
330 am EST Tuesday Jan 6 2009 


Short term...today 


After a clear and cold night, clouds will increase in coverage and 
thickness over Southeast Michigan today. There will be just enough filtered 
sunshine during the morning to help temperatures struggle toward 30f 
for afternoon highs at most locations, and the snow will hold off 
until late in the day and closer to the Ohio border. 


The 00z DTX and model soundings show the deep dryness that has been 
responsible for maintaining clear sky conditions since yesterday, 
and that will be our starting point for today. Several ripples in 
the strong upper jet over the Ohio Valley will then help with the 
high cloud increase over the region, along with the steadily 
eastward advancement of the upper trough over the plains. A stronger 
short wave from the Southern Plains will get surface pressure falls 
underway in the Ohio Valley and back the low level flow toward the 
east over the southern Great Lakes. This wind pattern will help 
maintain the supply of dry air in the low levels from the surface 
high as migrates into eastern Canada and the Atlantic coast. This 
dry air will delay the onset of snow in Southeast Michigan until very late 
in the day and mainly south of M-59. 


&& 


Long term...tonight through Monday 


00z models seem to be handling two upstream items of interest well 
when compared to current water vapor imagery. The first is the broad 
upper trough pushing out of the southwest and the other is the 
strong shortwave moving across Alberta. These two systems will phase 
east of The Rockies this evening...creating an amplified trough that 
will slowly move across the eastern U.S. Wednesday and Thursday. As 
this occurs...the surface low over the Texas Panhandle will merge 
with a broad area of low pressure stretching from Alberta into the 
northern plains...with the center settling over Northwest Ohio this 
evening. GFS/Euro in good agreement with spreading a broad area of 
weak isentropic lift up into lower Michigan this evening and 
overnight on the north side of the system...but keep the main area 
of baroclinicity to our south over Ohio and Lake Erie. Area of lift 
will be helped by some upper jet forcing...but we're really only 
expecting to see about an inch of snow fall across Southeast 
Michigan overnight. Surface low will lift northeast across Lake Erie 
and Lake St Clair on Wednesday...with the middle-level deformation axis 
settling in over the northern half of Lake Huron. This axis...along 
with a strong cold front will then push down across Southeast 
Michigan Wednesday night. Snow accumulations on Wednesday will be 
minimal...but will be followed by additional accumulations up to one 
inch as an area of snow develops just ahead of the front and within 
deformation zone overnight. In all...this storm system will really 
not bring too much snow to the region...with 2 to 4 inches falling 
within a 36 hour period from tonight through Thursday morning. 
Highest amounts are expected to occur across the Tri-Cities and 
thumb...where deformation will be the strongest and last the longest. 


Snow will transition to lake effect on Thursday as west to northwest 
winds and cold air advection continue behind the front. Breezy 
conditions on Thursday will combine with expected highs near 30 (at 
best) to produce wind chills in the teens or even single digits. The 
next storm system is expected to work across the Great Lakes late 
Friday through Saturday. Models had previously come to a strong 
consensus with taking the system through Ontario...but 00z Euro has 
flip-flopped back to a previous solution which takes it through the 
Ohio Valley instead. Will continue to favor solutions with the more 
northern track...such as the GFS/Gem/12z Euro. This makes snow 
likely Friday afternoon through Friday night...with potentially a 
few inches of accumulation. 


Surface high pressure will allow the area to dry out Saturday night 
and Sunday...however most noticeable weather for the weekend will be 
the cold temperatures that settle in over the region. Current 
expectations are for single digit lows both Saturday and Sunday 
nights...with highs on Sunday remaining in the teens. 


&& 


Marine... 


High pressure departing from the Great Lakes to the East Coast, and 
low pressure developing in the Ohio Valley, will lead to light winds 
turning toward the east today and tonight. A trough of low pressure 
will then settle over Southern Lake Huron during Wednesday 
separating stronger NE winds over the north half of the lake from SW 
winds over Lake St Clair and Lake Erie. The strongest winds in this 
pattern will be over Western Lake Erie but will be offshore. Small 
craft/brisk wind advisories may be needed by Wednesday night but the 
offshore component will keep gusts below gale force. By the time 
this system exits the Great Lakes on Thursday, the gradient flow 
will result in uniform northwest winds over all marine areas and looks weak 
enough for speed below gale force through Friday. 


&& 


Previous discussion...issued 1210 am EST Tuesday Jan 6 2009 


Aviation... 


VFR conditions will prevail with clear skies and light winds during 
the night...replaced by a gradual increase in middle/upper level clouds 
at or above 12kft later this morning. Clouds will further thicken/lower 
late in the forecast as a disturbance approaches from the 
southwest. Even then...ceilings will remain lower VFR (aoa 5000 
feet) until 22z-00z before light snow begins to work into the area 
during the evening and ceilings/visibilities trend towards 
MVFR...and IFR by 06z into the overnight. 


&& 


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


&& 


$$ 


Short term...bt 
long term....hlo 
marine.......bt 
aviation.....Dg 




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