Weather

645 
fxus63 kapx 281936 cca 
afdapx 


Area forecast discussion...corrected 
National Weather Service Gaylord Michigan 
335 PM EDT Thursday Aug 28 2008 


Synopsis.../issued at 332 PM/ 


Cold front runs from western upper/central WI/eastern Iowa at early 
afternoon...will continue to push east and across the rest of the 
state overnight. Showers and embedded thunderstorms associated 
with this front and its associated upper level disturbance will be 
the Last Chance for significant rainfall into early next week. 
Weak high pressure builds into the state by Saturday...followed by 
a nice warming trend for the latter half of the weekend and into 
the first week of September. 


Jpb 


&& 


Short term.../issued at 332 PM/...tonight 


Upstream shortwave and cold front bisecting the state of Wisconsin 
slated to move steadily east across the area tonight. While 
narrow...moisture tongue along and slightly ahead of these features 
rather impressive...with precipitable water values >1.5 inches and 850mb dew 
points in the lower teens celsius. Still thinking that rather 
strong convergence associated with frontal slope and pocket of 
healthy middle level -divq interacting with this moisture tongue will 
be able to kick off at least a broken line of showers and storms 
later this afternoon...which should pivot east through the 
overnight. Have maintained likely wording across the northern half 
of the area with passage of better dynamics...tapering to high 
chance south. Despite decent moisture...instability profiles 
meager at best (most unstable cape profiles a couple hundred 
j/kg)...owning to sub 5.0 c/km middle level lapse rates. Thus...still 
thinking showers will be the dominate precipitation type...with just some 
embedded rumbles of thunder. Latest day 1 Storm Prediction Center severe weather 
outlook still places the northwest quadrant of our County Warning Area under a 
slight risk. Hard to argue with at least the 
potential...especially this evening...with eastern extent of 40 to 
50 knot 0-6km bulk shear magnitude bullseye managing to sneak into 
this area prior to frontal passage. Still...given such weak 
instability...thinking potential is isolated at best...and will 
remained confined to possible 60 miles per hour wind gusts with any bowing 
segments within convective line. Otherwise...models in decent 
agreement with frontal timing...and as such...have greatly trimmed 
back probability of precipitation from west to east as the front traverses the 
landscape... with northwest lower and eastern Upper Michigan 
drying out after midnight. 


Msb 


&& 


Long term.../issued at 332 PM/...Friday and beyond 


Friday...cold front clearing the area around daybreak should bring 
best rain chances to an end. Cooling aloft will be offset somewhat 
by stronger subsidence setting in during the afternoon...but deep 
layer mixing anticipated (beyond the 800mb level) which should allow 
for some cumulus development but not expecting things to get too out of 
hand even with some lake breeze convergence setting up during the 
afternoon...as drier air mixes into the cbl. Another short wave 
trough forecast to clip Lake Superior Friday night...guidance 
remains consistent in keeping deeper moisture to the north with just 
some ac/altocumulus castellanus moving into northern portions of the forecast area 
overnight. 


Saturday...weak frontal boundary associated with aforementioned 
short wave trough will settle into the forecast area Saturday...but 
other than a band of middle cloud associated with departing short wave 
trough the boundary expected to come through dry with just a wind 
shift. High temperatures across northern lower should climb into 
the 80s as the warm weather begins to build. 


Extended forecast (sunday through thursday)...amplifying long wave 
pattern over North America will bring September in a-blazin'...so to 
speak...with upper ridging and hints of a closed high developing 
over the western Great Lakes for the first part of next week. Will 
continue to trend highs upward...introducing some 90 degree highs 
into the mix for Monday through Wednesday. This is well above both 
climatology and guidance numbers...but in the pattern as forecast it 
should get progressively a bit warmer each day as mixed layer depth 
increases and soils dry out further. Record highs in the Tuesday/ 
Wednesday time frame mostly date back to 1953...mainly middle 90s with 
upper 90s at apn (including 99 on the 1st). Looking back at the 
reanalysis data for the first week of September 1953 does show 500mb 
heights 10-30m lower than those forecast for next week. But 850mb 
temperatures were widespread above 20c and current medium range 
guidance remains generally below 20c through Wednesday. So won't go 
hog wild though the record high at the Soo on Tuesday is only 87 and 
should be in jeopardy if the pattern progresses as forecast. A 
weakening cold front is still forecast to try and push into the 
state during the midweek period...not even sure at this point if 
this feature will have enough moisture with it to generate rainfall. 
Will move current rain chance in wednesday's forecast ahead one 
day...thus having a dry/warm forecast through midweek. Will 
continue to carry a mention of elevated fire danger through the 
first half of next week in the afternoon severe weather potential statement. 


Jpb 


&& 


Marine.../issued at 332 PM/ 


Anticipated Small Craft Advisory wind gusts have failed to materialize yet 
this afternoon across the waters bordering northeast lower and 
eastern Upper Michigan. With more stable evening hours 
approaching...have a hard time justifying current Small Craft Advisory headlines. 
Will continue to monitor observation and make final call at necessary 
release time. Winds go northwest behind frontal passage. 
However...upstream observations show wind fields remaining weak 
under modest cold air advection. Thus...thinking any wind gusts will remain sub 
advisory. 


Cold front expected to be through the marine areas shortly after 
daybreak Friday. Only real threat for small craft conditions will 
come Friday morning right behind the cold front where isallobaric 
gradient may locally increase wind speeds. Gradient relaxes by 
afternoon and will likely see some lake breeze component develop. 
Southwesterly breezes will pick up Saturday on lakes Michigan/ 
Huron...weak cold front dropping into Upper Michigan will likely shift 
winds more to the northwest on Whitefish Bay. But headline 
conditions not expected Saturday. 


Msb/jpb 


&& 


Aviation.../issued at 144 PM/...valid for 18z tafs 


Difficult taf cycle as narrow moisture channel interacts with 
approaching shortwave and associated cold front later this 
afternoon and evening. Still thinking a broken line of showers... 
with embedded thunderstorms...will develop this afternoon and move 
southeast across the taf sites through the early morning hours. 
Giving difficulty in predicting exact thunderstorm evolution and 
strength in marginal unstable environment...decided to run with cumulonimbus 
qualifier without explicitly mentioning thunder in the tafs. Will 
keep all conditions VFR category (early exception at kapn with 
lingering low overcast) at this time. Front slated to clear the 
area towards Friday morning. 


Msb 


&& 


Apx watches/warnings/advisories... 
Michigan...none. 
Lm...none. 
LH...none. 
Ls...none. 


&& 


$$ 

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