Area forecast discussion
National Weather Service Green Bay WI
435 am CDT Wednesday may 22 2013
Forecast discussion for routine morning forecast issuance
Synopsis...
issued at 425 am CDT Wednesday may 22 2013
Upper low digging down the West Coast will kick the upper trough now over
the plains eastward toward New England...resulting in a highly
amplified but fairly stable upper pattern across the Continental U.S. For much of
the period. By late in the period...the western trough will start to
expand eastward as strong Pacific jet heads into California.
Temperatures will start out below normal...then moderate during the second
half of the forecast period...likely to above normal levels by the
middle to end of next weak. The main precipitation event will occur early as
plains upper trough crosses the region. That system will be a good precipitation
producer...especially for the southeast part of the forecast area.
&&
Short term...today...tonight...and Thursday
issued at 425 am CDT Wednesday may 22 2013
General forecast for the short-term is fairly simple. Upper trough from the
northern plains will shift eastward across the area and phase with some energy
digging southeast from Canada...resulting in strengthening cyclone
tracking across southern WI this aftn/tngt. That system will bring a
widespread soaking rain to most of the forecast area this aftn/tngt.
Main challenge is working in the forecast details.
Just some lingering light rain showers over the far north early this morning.
Otherwise...the forecast area experiencing a lull in the precipitation. Surface
boundary was over northern WI at 05z...but has since slipped southward along
the lake and Bay. Fog...some of it quite dense...was over the lake
and Bay. The passage of the boundary allowed the fog to advect
inland...with visibilities now as low as 1/4 sm at times at the grb
Airport. Thinking is that the real dense fog will be confined
fairly close to the water...and won't be widespread enough to
warrant an advisory. Will cover with an Special Weather Statement...which is already out.
Satellite imagery already showed expanding area of colder cloud tops
liftg NE across Iowa/southeastern Minnesota. Not much in the way of radar returns
with this feature yet...but it should eventually evolve into the
comma head that will pivot across the area late tda/tngt. Ran probability of precipitation up
to categorical in the southeast 2/3 of the forecast area. Upped precipitation amnts
considerably from previous forecast. Although instability will be limited...
there may be enough to generate some thunder this aftn/eve.
Carried some thunder in the forecast...but limited it to isolated
coverage. Maximum temperatures will probably occur mid-day...before rain
becomes widepsread.
Winds will increase late today and this evening. Some concern we could
have one of those situations where strong NE winds cause water to
back up the Bay toward the mouth of the Fox River. On the other
hand...the limited potential for thunderstorms should prevent
excessive rainfalls. Also...didn/T get much rain in east-c WI
yesterday...so at least we aren/T starting with high flows coming into
the mouth of the Fox.
Precipitation shield should start to push to the southeast after midnight. Shut
down precipitation in far north-c WI by late tonight. Kept it going over far east-c
WI early Friday...though it shouldn/T last too long into the morning.
Strong subsidence and the arrival of drier air should scour out clouds
from northwest-southeast Friday morning. Desite the expectation of near full sun Friday
afternoon...temperatures and strong northerly winds will make it feel chilly for late
may.
Long term...Thursday night through Tuesday
issued at 425 am CDT Wednesday may 22 2013
Below normal temperatures will continue into the Memorial Day
weekend then trend at or slightly above normal for early next
week. Thursday night will be cold with a widespread frost or
freeze north and west of the Fox Valley. A hard freeze should be
expected for locations north of a Wausau to Marinette line. Latest
numerical guidance suggest temperatures in our typical cold spots
like Land O Lakes...Tomahawk and Merrill could drop down into the
lower to middle 20s. With such a dry air mass in place...clear
skies and light winds...would not be out of the question that Land
O Lakes drops into the upper teens. Leaned toward the colder
guidance north and west of the Fox Valley due to winds becoming
light and variable after sunset. Across the Fox Valley the winds
will remain up a bit little longer during the night...therefore
temperatures should fall into the middle to upper 30s. Would not
take much if winds went calm for a while that this region
approached 32 degrees. Will let day shift have the privilege of
issuing the freeze watch. Despite temperatures in the 20s and 30s
Thursday night...high temperatures will climb back into the lower
to middle 60s at most places on Friday. Afternoon relative
humidities will drop to 10 to 20 percent across the north...and 20
to 30 percent across the south.
Models continue to differ on northward extent of the clouds and
precipitation later Friday night into Saturday. Have lowered min
temperatures due to slower arrival of the clouds. Frost is likely
again Friday night across portions of north-central and far
northeast Wisconsin. GFS BUFKIT sounding very dry on Saturday...
thus would only expect sprinkles across our far southwest. The
differences in the models continue for the rest of the Memorial
Day weekend as GFS/Canadian try to edge precipitation back into
our southwest counties at times on Sunday into Memorial Day. The
European model (ecmwf) on the other hand drives the front well south and keeps US
dry through Tuesday. Did not make much changes to the Sunday
through Tuesday period due to the uncertainty on the different
model solutions. Would have prefer ed to remove precipitation
Sunday and Memorial except over our very far southwest.
&&
Aviation...for 12z taf issuance
issued at 425 am CDT Wednesday may 22 2013
LIFR ceilings across the north this morning...and some LIFR/vlifr
conditions in fog near the lake and Bay. Though some improvement
is expected...overall poor flight conditions will linger across the north
into tonight. Poor flight conditions...mainly due to low ceilings...will
develop across the rest of the area as well this aftn/eve. May need
low level wind shear due to very strong NE flow just above the surface over east-c WI
tonight...will make issuance time decision on that.
&&
Marine...
issued at 425 am CDT Wednesday may 22 2013
With high-end Small Craft Advisory winds looming just on the
horizon...opted to start the Small Craft Advisory immediately and
just wrap the current marine fog event into it. Details and
expected conditions will be spelled out in the forecast and mww
product...so opted to keep actual headline simple.
&&
Grb watches/warnings/advisories...
none.
&&
$$
Synopsis.......skowronski
short term.....Skowronski
long term......eckberg
aviation.......skowronski
marine.........Skowronski
