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Area forecast discussion
National Weather Service Green Bay WI
241 PM CDT Friday Apr 18 2014
Forecast discussion for routine afternoon forecast issuance
Short term...tonight and Saturday
issued at 239 PM CDT Friday Apr 18 2014
Main forecast issues to be timing of precipitation onset across the north on
Sat as a system begins to affect the region. Temperatures on Sat are also
no bargain as clouds thicken...plenty of snow on the ground across
the north and winds off of Lake Michigan.
The 19z msas surface analysis indicated a ridge of hi pressure extended from
western Ontario southward through WI to the middle-MS valley. Morning low clouds
in the east had mixed out and dry air mass overhead was eating
away at the middle/hi clouds trying to advance from the west. Vsbl
satellite imagery clearly shows the snow line running roughly from
Medford to Antigo to Wausaukee.
The surface ridge axis slides toward the eastern Great Lakes tonight and allows
the wind to slowly veer to the east-southeast overnight. Attention to be focused
over S-central Canada/northern plains where a surface low/cdfnt/shortwave trough
to be situated. Increasing southerly winds (50-60 knots low-level jet)
to be aimed at the upper MS valley and help lift a warm front into central
Minnesota/SW WI by daybreak. Expect to see some precipitation break out in the
strong isen lift regime/upper diffluent flow over Minnesota and move into northwest
WI late. For NE WI...we should remain dry through the night although a
small pop may be needed for Vilas/northwest Oneida counties late. Under
increasing clouds...min temperatures to range from the upper teens/lower 20s
under the snowpack north...to around 30 degrees central/E-cntrl WI.
The surface low and shortwave trough are forecast to move along or just
north of the U.S.-Canadian border on Sat. As this occurs...the
cold front will slowly push across Minnesota as the warm front lift NE through WI. Even
though the low-level jet weakens...a persistent south wind just above
the surface will bring moisture northward. This scenario would keep stronger
forcing well to our northwest with the shortwave trough...leaving the cold front
as the primary focus for precipitation. This would place north-central WI with
the best chance of seeing light rain move in on Sat. The rest of the
forecast area will only see clouds increase/thicken during the day with
warmer temperatures. Readings are expected to reach the upper 40s over
north-central WI...to the lower to middle 60s over parts of central WI. Onshore
winds will continue to keep areas near the Bay and lake cooler.
Long term...Saturday night through Friday
issued at 239 PM CDT Friday Apr 18 2014
Models are in a little better agreement now about the
weak cold front that will move into Wisconsin Saturday night and
then stall somewhere in southern Wisconsin Easter Sunday. Think
there is a good chance of showers moving from northwest to
southeast late Saturday night and Sunday morning with perhaps a
break in the action Sunday afternoon and evening before the next
few rounds of showers arrive from the southwest. Northcentral
Wisconsin looks to have the best chance of staying dry Easter
Sunday. The front should exit the area Monday afternoon or evening.
Then upper ridging arrives for Tuesday through Wednesday with dry
air and near seasonable temperatures. There is a little better
agreement between the medium range models for the upper system
approaching from the plains states Thursday. They bring the upper
system across Wisconsin Thursday night and Friday with a good
chance of rain possibly changing to snow before ending.
Melting snow will continue to cause rivers and streams to slowly
rise Saturday through Monday. Rainfall Saturday night through
Monday will also contribute to rising water levels. Rainfall
amounts are a bit more modest that what was forecast a few days
ago...which may spare US from significant flooding.
Aviation...for 18z taf issuance
issued at 1233 PM CDT Friday Apr 18 2014
Now that the morning MVFR low clouds have mixed out...
expect to see only middle/hi clouds drift through at times this afternoon
and evening. Main attraction to be a Pacific system moving across
southern Canada/northern tier of states this weekend accompanied by a cold front.
Increasing southerly winds aloft tonight/Sat will bring moisture northward for
the cold front to generate showers to our west tonight and the northern third of
WI on Sat. Even with the system approaching...flying conditions
should remain VFR through Sat with VFR cumulus field expected to develop
by Sat afternoon.