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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Thursday
• 
• High: 90 °
• Low: 55 °
• T-Storms

• Friday
• 
• High: 79 °
• Low: 57 °
• Chance of T-Storms

• Saturday
• 
• High: 75 °
• Low: 48 °
• Chance of T-Storms

• Sunday
• 
• High: 97 °
• Low: 66 °
• Partly Cloudy

• Monday
• 
• High: 79 °
• Low: 48 °
• Chance of T-Storms

Area forecast discussion 
National Weather Service Green Bay WI 
1019 PM CDT Wednesday may 23 2012 


Updated aviation portion for 06z taf issuance 


Update...forecast focus obviously on the next 24-36 hours. Models all 
now pretty much in agreement that strong compact deepening cyclone will 
track from western Iowa at 12z to around dlh by 00z...then across Western Lake 
Superior tomorrow evening. Strength of the system will result in 
very strong wind fields...while deepening nature should result in strong 
directional turning with height. So kinematics very favorable for severe 
weather. Question will be buoyancy...and that will come down to moisture. 


00z grb and ilx soundings about as dry as you/ll see for as warm 
an air mass as we have across the region. Some moisture was flowing 
toward the area from the Ohio Valley...but that will get shunted east as 
flow veers more to the S. Modest moisture had pooled along the 
front...but middle 50-low 60f dewpoints nothing special for late may. And 
southerly low-level flow into the area tonight/Thursday will continue to originate in 
band of dry air with surface dewpoints in the 30s-40s f that stretched from 
WI across Illinois/southeastern MO and into northern Arkansas. That was topped by 10-40 percent 
relative humidity/S at 850 mb...so the air aloft is dry too. Best guess is that 
moisture pooled along the front will work into the far western/northwestern part 
of the forecast area tomorrow afternoon...and that greatest risk of severe will 
be there. Best chance for severe across the rest of the area will be if line 
of convection can organize along the cold front and then sweep 
east...bringing strong synoptic scale winds down to the surface. If that 
scenario plays out...could get damaging gusts from relatively 
weak thunderstorms...or even just with showers. 


Another concern is wind speeds in general tomorrow/tomorrow night. 
Expect S winds of 20-30 miles per hour with gusts to around 40 miles per hour across the 
area from late morning through afternoon. But main concern is tomorrow 
evening. Cold front surging eastward around deepening cyclone seems like 
a classic set-up for burst of sig Post-frontal winds as cold air advection 
allows strong winds to descend to the surface. Updated severe weather potential statement to mention a 
brief period of 40-50 miles per hour winds right behind the cold front. That 
would be Thursday evening across most of the area...but could be a little 
after midnight in the far east. Winds should begin to slowly subside 
later in the night. 


Updated product suite of grids/zfp/hwo already out. Also posted 
top news story about winds and conditional nature of severe 
potential. 


Skowronski 
&& 


Previous discussion...issued at 607 PM CDT Wednesday may 23 2012... 


Short term...tonight and Thursday. Main forecast issue will be the severe 
weather threat headed into Thursday afternoon as a cold front moves into western 
WI accompanied by favorable moisture...mid-lvl forcing and upper-level 
lift. 


The 19z msas surface analysis showed a large area of hi pressure over the 
eastern Great Lakes. A cold front stretched from the ND/Minnesota border southward into 
eastern Nebraska. A tight pressure gradient was bringing some gusty winds 
to the Midwest with dew points climbing into the 50s as far north as 
southern Iowa. Radar mosaic was picking up showers/thunderstorms from SW to NE Minnesota 
with most of the storms behaving themselves thus far. 


A broad upper trough moves across The Rockies tonight while the eastern Continental U.S. 
Upper ridge hardly moves. The cold front slowly pushes across Minnesota tonight with 
several shortwaves riding NE and a coupled jet structure situated 
over the upper MS valley. Most of the precipitation should be confined from 
the western third of WI westward where better focus (cdfnt)...lift 
(jet/fnt) and deeper moisture to co-exist. There is a possibility 
for a rogue shower/isolated thunderstorm to push toward north-central WI late 
tonight...so may need to carry a minimal pop there. Otherwise...the 
rest of the forecast area will remain dry under a veil of middle and hi 
clouds. Temperatures tonight will be much milder than last night not only due to 
the clouds...but the strong winds aloft as 925 mb winds to reach 
40 kts. Look for readings to only drop into the 55 to 60 degree range 
throughout all of NE WI. 


A potentially active day on tap across the western Great Lakes/upper MS 
valley on Thursday as the upper trough strenghthens due to a middle-level speed 
maximum...a surface wave develops on the cold front and moves north-NE to near 
iwd...and gusty S-SW winds bring Gulf moisture into WI. Lesser amounts 
of clouds across the eastern half of WI Thursday morning will allow for temperatures 
to easily rise through the 70s...eventually reaching highs in the 
lower to middle 80s. Gulf moisture to steadily increase through the day with 
dew points reaching the middle 50s in the afternoon. Convective available potential energy should reach 
around 1k j/kg as lifted indice's drop to around -4. The cold front will not move 
much on Thursday due to the surface wave moving along it...with most models 
still placing the boundary over western WI at 00z Friday. Models are also 
indicating strong shear in the 0-6 km above ground level with values greater than 
75 kts which will help provide some rotating updrafts. Expect to see 
thunderstorms develop/intensify over western WI Thursday morning and make an eastward push 
into central WI during the afternoon. Storm Prediction Center does have most of NE WI in 
a slight risk of severe weather Thursday afternoon/evening and with the 
variables listed above...hard to argue. Through the daylight hours... 
hail and damaging wind gusts would be the primary threats. 


Long term...Thursday night through next Wednesday. 


Main issues this period on precipitation Thursday night and again during the 
Memorial Day weekend. Some potential for severe with 
thunderstorms...especially Thursday evening. 


Southwest upper pattern into the weekend...shifting to more zonal 
or northwest flow for next week. Some difference on the models 
with strength of eastern U.S. High and speed of frontal movement 
for the weekend. Little change made to previous extended...keeping 
categorical probability of precipitation over central portions of County Warning Area on Thursday evening. 
Lowered probability of precipitation/quantitative precipitation forecast a bit along the Lakeshore as main energy/surface wave 
lifts north through Western Lake Superior. Instability not overly 
exiting...but sheer and strength of low level winds quite 
impressive. Front GOES through around midnight with high pressure 
building in on Friday. 


For the Holiday weekend...warm front begins to lift north reaching 
the Illinois/WI border Sat morning. Front to continue north reaching far 
northern WI Sun morning. With warm front north and cold front 
still to our west...sun looks like mainly dry and warm day. Cold 
front moving through late Sun night/morning morning will limit severe 
threat. High pressure builds in for Tuesday/Wednesday with temperatures returning 
to normal or below normal. 


Marine...some differences between models on low level wind speeds with 
NAM showing 70 kts at 925mb and Euro at 45kts. All models do 
agree on remaining strong Thursday afternoon and night keeping the 
strong winds from surfacing over the lake. Will issue strong small 
craft at this time. 
&& 


Aviation...for 06z taf issuance. Little change to forecast logic for 
this issuance. VFR conditions expected the Thursday afternoon. Low level wind shear 
will continue tonight...with strong gusty S winds expected during the day 
tomorrow as we mix. Squall line will probably develop to our west 
tomorrow afternoon...and sweep eastward across the area between 23z/23 and 05z/24. 
Should have brief surge of strong SW winds right behind the cold 
front. 


Skowronski 
&& 


Grb watches/warnings/advisories... 
none. 
&& 


$$