Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 171946
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
246 PM CDT Thu Aug 17 2017

Forecast discussion for routine afternoon forecast issuance

.SYNOPSIS...
Issued at 245 PM CDT Thu Aug 17 2017

Lingering showers tonight, then generally dry with a warming trend
into the weekend.

The band of westerlies across the northern CONUS and southern
Canada will remain progressive as it gradually strengthens and
loses amplitude through early next week. Reamplification will
occur late in the period as a ridge builds over the Plains and a
trough strengthens from eastern Canada into the Great Lakes
region.

Temperatures will start out seasonable and then trend upward,
probably peaking at 5 to 10 degrees above normal by late in the
weekend and early next week. Readings will drop back (probably to
near or a little below normal) as the upper flow tilts northwest
due to amplification next week. The main opportunity for
precipitation will be with a frontal system crossing the area early
next week. That system will probably be a significant
precipitation producer as ample moisture and upper support will
accompany the FROPA, and likely be sufficient to result in above
normal amounts for the period.
&&

.SHORT TERM...Tonight and Friday
Issued at 245 PM CDT Thu Aug 17 2017

Occluded low pressure system and deep upper trof will exit the
region this evening, resulting in decreasing showers from
southwest to northeast. The threat of thunder has nearly ended,
with instability only lingering in the very far northeast part
of the CWA. Have pulled any mention of thunder from the forecast
after 20z.

Widespread low clouds will continue through the night and into
Friday morning before eroding as the cyclonic flow weakens and a
weak ridge of high pressure arrives. Gusty west to northwest
winds will continue through the night and Friday morning before
diminishing. Have extended small craft advisories through 18z
Friday. The best forcing associated the next short-wave trof will
stay to our southwest on Friday afternoon, so will carry a dry
forecast.

Used a blend of the better performing guidance sets for
temperatures. This resulted in lows in the upper 50s and lower
60s tonight, and highs in the lower to middle 70s on friday.

.LONG TERM...Friday Night Through Thursday
Issued at 245 PM CDT Thu Aug 17 2017

Light precipitation with a shortwave passing to our south may
graze the southwest portion of the area Friday night, but that
does not look like a significant precipitation event. Generally
quiet weather is likely during the weekend as high pressure passes
south of the area and shortwave ridging slowly moves through
aloft.

The main weather producer during the period will likely be the
front crossing the area early next week. The models suggest a
significant return of moisture is likely to occur ahead of the
front. The overall loss of amplitude to the westerlies also
suggests relatively fast flow will be in place aloft. So the large
scale pieces seem to be in place for a round or two of strong and
possibly severe storms. But the actual severe threat will
obviously depend on the details of the pattern that are unknown
this far in advance.

At least a few days of quiet weather are likely as northwest
upper flow and high pressure settle over the area during the
latter part of next week.

Timing differences exist among the models, especially pertaining
to precipitation with the system early next week. But those are
impossible to resolve at this point. The standard forecast
initialization grids based on a broad blend of model output seemed
reasonable, so no significant chances were necessary.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1236 PM CDT Thu Aug 17 2017

A surface low was shifting into north central WI early this
afternoon, with a trailing cold/occluded front moving through
central WI. light to moderate showers were developing near and
ahead of this frontal system, but thunderstorm activity has been
minimal so far. Although conditions had improved to VFR over
parts of eastern WI, expect most of the CWA to have MVFR/IFR
conditions through mid-morning Friday, with a return to VFR most
locations by the end of the TAF period.

Gusty southwest to west winds will develop across central and east
central WI this afternoon and evening, in the wake of the frontal
passage. Though not as strong, brisk west-northwest winds will
persist overnight into Friday.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement until 9 PM CDT this evening for WIZ022-
040-050.
&&

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Kieckbusch
LONG TERM......Skowronski
AVIATION.......Kieckbusch



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