Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 261137
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
637 AM CDT Thu Apr 26 2018

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Friday
Issued at 417 AM CDT Thu Apr 26 2018

Precipitation trends and temperatures are the main forecast
concerns.

A cold front extending from northern MN into the eastern Dakotas
will shift southeast, reaching north central WI early this
afternoon, and east central WI this evening. Ahead of the front,
temperatures will warm into the 60s, with relative humidity
dropping into the 20 to 30 percent range. The mild and dry
conditions, coupled with moderate southwest winds may result in
elevated fire danger in grasses and other fine fuels, so residents
should not attempt to burn yard waste.

Although no precipitation is currently occurring with the front,
at least a narrow band of post-frontal showers is expected to
develop as it moves through GRB CWA this afternoon/evening.
Temperatures will cool back down in the wake of the front
overnight, with lows dropping into the upper 20s north and 30s
elsewhere.

A clipper low pressure system will track just southwest of the
forecast area on Friday and spread precipitation into the
region during the morning. Temperatures will be cold enough for
a period of light snow during the early to mid-morning, with
potential for an inch or less of accumulation over mainly north
central WI. Have bumped pops up to likely or categorical over much
of the forecast area during the late morning and afternoon. Also
trimmed back the chance of thunderstorms, confining the mention
to only the southwest half of the forecast area, where mid-level
lapse rates will be steepest. High temperatures will be much
cooler, in the 40s and lower 50s.

.LONG TERM...Friday Night Through Wednesday
Issued at 417 AM CDT Thu Apr 26 2018

500mb ridge will build across the region late in the weekend as an
upper trough continues to deepen across the western United States.
The upper trough is expected to continue to deepen early next
week. In response, a southwest flow pattern will develop across
the western Great Lakes. This pattern usually brings milder and
wetter conditions to the area. This may be the case next week
which could renew flooding concerns on area rivers if heavy rain
materializes.

For Friday night, continued a small chance of showers during the
early evening hours as system departs the area. There could be
a period of gusty winds from the north behind the system. This
would be more of a marine concern for small crafts. High pressure
is expected to dominate the weather pattern over the weekend,
bringing dry conditions with very low relative humidity readings.
The dry weather should last into Sunday evening as the high moves
off to the east. The forecast becomes muddled on Monday as the
ECMWF is consistent in bringing a chance of showers and perhaps
storms with 500mb disturbance. The cloud cover and rain would
significantly impact high temperatures during the period. Due to
uncertainty in the precipitation chances Monday, continued the
previous forecast on high temperatures.

On Tuesday, the models would suggest we would have the warmest day
of the year so far with highs in the 70s and dewpoints climbing
into the 50s to near 60. A cold front will be moving into the
region during the day Tuesday and across the area Tuesday evening.
It now appears there may be a window of opportunity for severe
thunderstorms Tuesday afternoon and evening. Model guidance
was indicating steep mid level lapse rates, 0-6 km shear values
of 35 to 45 knots, total totals in the 50 to 55 range along with
a fairly impressive jet streak moving across the area to aid in
the lift. Some of the thunderstorms could produce damaging winds
and large hail, especially if the ECMWF slower solution plays out.
It is still 6 days out, so a lot can change between now and then,
thus will watch it over the next several days to see the risk of
severe weather increases. Beyond Tuesday night, models in good
agreement bringing another wave of low pressure into the region
Wednesday into Thursday. This feature would also have the
potential for heavy rain if it materializes.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 628 AM CDT Thu Apr 26 2018

VFR conditions are anticipated over most of the forecast area
through the TAF period. The exception may be over far north
central WI late tonight. A cold front will move through the region
during the afternoon and early evening, followed by a narrow
band of post-frontal showers. The showers should exit eastern WI
by midnight. A clipper low pressure system will approach the
region late tonight, and may bring some light snow to far north
central WI.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM.....Kieckbusch
LONG TERM......Eckberg
AVIATION.......Kieckbusch


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