Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 202343
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
643 PM CDT Wed Mar 20 2019

Updated aviation portion for 00Z TAF issuance

.SYNOPSIS...
Issued at 229 PM CDT Wed Mar 20 2019

Relatively quiet weather expected for the next week. Temperatures
will be fairly close to seasonal normals, with just some
scattered light precipitation at times.

The blocky pattern over western North America and the eastern
Pacific will undergo some changes in structure during the next
week, but basically remain in place. The main change across North
America will be a gradual strengthening of the southern stream
undercutting the block, though the bulk of the energy in the
southern stream will remain south of the area during the period.

Temperatures will undergo day to day variation, cooling to
somewhat below normal with the arrival of each fresh surge of
polar air and then warming to a little above normal as the air
mass moderates and the associated anticyclone departs off to the
east. The forecast area remaining between the main branches of
the flow or dominated by the northern stream favors only scattered
light precipitation at times.
&&

.SHORT TERM...Tonight and Thursday
Issued at 229 PM CDT Wed Mar 20 2019

A compact shortwave with strong QG forcing will swing through the
remainder of the area this evening. Will carry fairly high PoPs
for the remainder of the afternoon, then taper them back during
the evening. P-Type will be a mix of rain and snow, with perhaps a
bit more snow than normal given the observed surface temperatures.
The frozen precipitation may be graupel across the southern part
of the area. Trended toward a little cloudier forecast for the
remainder of the night than we previously had going, as clouds
were rather extensive on mid-afternoon satellite imagery.

Some of the hi-res guidance was producing light precip over
north-central Wisconsin Thursday afternoon as the next northern
stream shortwave arrives in the area. Opted to carry that as just
a trace event for now as the best forcing will pass through to the
north.

Based temperatures on a blend of recent top performing guidance
products, with some adjustments for recent biases.

.LONG TERM...Thursday Night Through Wednesday
Issued at 229 PM CDT Wed Mar 20 2019

A relatively quiet pattern will be in place across the region over
this period, thanks to strong ridging over northwest North America,
and split flow across the CONUS, which will keep southern stream
systems south of the region for the most part.  The only chance of
widespread precipitation looks to occur on Sunday when a southern
stream storm system attempts to push into the western Great Lakes.
No clear model preference for this forecast cycle, so will use a
blend of the gfs and ecmwf.

Thursday night through Friday night...Northwest flow will be
overhead during this period, while surface high pressure moves from
south-central Canada on Thursday night and into the Great Lakes by
Friday night.  Some clouds may linger along and behind a cold front
on Thursday evening, but moisture is relatively shallow and the
airmass is not all that cold behind it.  Therefore cannot see much
more than a few flurries near the U.P. border. Conditions should
should turn more blustery by late Thursday night into Friday morning
when a secondary shortwave dives across northern Michigan.  Colder
air should be moving in by this time, which could bring in some snow
showers off Lake Superior and into far northeast WI and the Door
Peninsula.  Should then see decreasing clouds on Friday afternoon
into Friday night with the arrival of the surface high.  High temps
should fall back into the 30s on Friday across northern WI.  Clear
skies and light winds will set up a chilly night.

Rest of the forecast...The high pressure system looks to hang around
on Saturday and most of Saturday night.  Will then be watching the
movement of a southern stream storm system for late Saturday night
into Sunday.  This system will try to move into a very dry airmass
over the Great Lakes and possibly interact with a northern stream
cold front.  If precipitation does overwhelm the dry air that will
be in place, amounts should be relatively light, perhaps a tenth to
a quarter inch at most.  But the air originating out of a strong
high to the north could very well keep precip south of the area.
Canadian high pressure will then build into the region for early
next week, and push temps below normal while keeping the area dry.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 642 PM CDT Wed Mar 20 2019

Scattered rain showers will slowly diminish late this evening
from west to east as a shortwave and cold front passes through the
area. MVFR to IFR ceilings can be expected through much of
tonight before slowly improving throughout the day Thursday from
west to east. Downsloping westerly to northwesterly winds over
the eastern TAF sites may help to keep ceilings in the MVFR range.
&&

.HYDROLOGY...
Issued at 229 PM CDT Wed Mar 20 2019

The forecast weather conditions for the next week may be about as
favorable as we could possibly get to minimize the flooding risk.
The snow cover over the far southern part of the forecast area
(south of KY50-KATW-KGRB-KSUE) is pretty much gone as far as
holding significant water that will melt into runoff. So the
concern in these areas is mainly water backing up due to ice jams
as the ice breaks up on the rivers. Areas farther north still
need to melt a lot of snow/ice and move the water through the
river systems. Conditions during the next week will be favorable
for slow melting that will pose a minimal risk of flooding in the
short-term. The down side of that of course is that the prospect
for more serious flooding still exists at a later time, especially
if much warmer weather arrives along with significant rainfall.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......MPC
AVIATION.......Cooley
HYDROLOGY......Skowronski


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