FXUS63 KGRB 210337
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1037 PM CDT Mon May 20 2019

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Tuesday
Issued at 242 PM CDT Mon May 20 2019

The main forecast issues center around frost/freeze tonight and
how fast to introduce the next chance of rain showers to central
WI Tuesday afternoon. 

The 19Z MSAS surface analysis showed high pressure over the Upper
MS Valley. The cold front that moved through the area yesterday
had made its way to the Ohio Valley, but has begun to stall.
Visible satellite imagery indicated instability cu field over the
southeast half of WI, while the northwest half of the state had
started to clear out.

Any daytime cumulus clouds are expected to disappear early this
evening with the loss of daytime heating, along with winds
becoming light and variable. High pressure to stretch from western
Ontario southeast into the Great Lakes tonight with only some high
clouds overhead from our next system organizing over the southern
Plains. The air mass aloft is rather cool by late May standards
and with light winds, temperatures will fall into the upper 20s to
lower 30s north, upper 30s to lower 40s south. There could be some
patchy frost over the colder spots of central WI, but not
widespread enough to warrant a headline. Northern WI will see the
frost/freeze, however since the growing season has not officially
commenced, no headlines will be issued. That being said, anyone
with sensitive plants in northern or central WI may want to bring
them indoors or cover them tonight.

The high pressure is forecast to slide toward the eastern Great
Lakes on Tuesday and this will allow for our next system to lift
northeast into the central Plains/mid-MS Valley. Clouds are
expected to gradually increase across northeast WI with a chance
that the leading edge of WAA-induced light rain showers could
reach central WI by late afternoon. A dry feed of air from the
departed high pressure should slow the advance of the rain, thus
the bulk of the precipitation will likely hold off until Tuesday
night. Max temperatures to range from the middle 50s near Lake MI,
to the lower to middle 60s north (more sunshine initially).

.LONG TERM...Tuesday Night Through Monday
Issued at 242 PM CDT Mon May 20 2019

Main concern in the extended forecast will be the potential for 
additional rainfall and continued elevated flows on area rivers. In 
addition, temperatures are expected to warm to above average levels 
for the last half of the work week with increasing chances for
thunderstorms.

Tuesday night and Wednesday: Broad/dry high pressure will steadily 
slide off to the east/northeast of the area Tuesday night. Dry air 
will continue to filter into the area on east winds through the 
evening hours, which will likely slow the onset of the next batch of 
rainfall poised to move in late Tuesday night into Wednesday. A 
strong surface low and upper-level low is expected to lift from the 
central Plains Tuesday night, to the northern Plains by Wednesday 
afternoon. As this happens, a warm front will lift northward and 
through much of WI through this time period. Increased moisture flow 
into the area, along with isentropic upglide/forcing on WAA, will 
lead to increasing chances of showers and Thunderstorms. This will 
be mainly late Tuesday night into early Wednesday. Added forcing 
from the left-exit region of an upper-level jet will help to 
evacuate mass from the atmosphere in the upper levels, leading to 
increased broad scale forcing. The area will be under the dry slot 
Wednesday afternoon, which will allow for a brief break in the 
precipitation coverage, although some isolated to 
showers/thunderstorms may develop later in the day, especially west 
and north-central. Most locations can expect to see around a half 
inch of rainfall, except higher amounts near any thunderstorms. 
Outside of showers and thunderstorms, warmer temperatures are 
expected to advect northward with most locations warming into the 
mid/upper 60s to low 70s for Wed. afternoon. Tuesday night lows will 
be mainly in the 40s.

Wednesday night into Thursday: The aforementioned low pressure 
centers are expected to shift eastward, crossing northwest WI and 
much of Upper MI. The better/deeper moisture and better forcing will 
lift north of much of the CWA, keeping most of the showers and 
thunderstorms across northern MN/Upper MI/Lake Superior for this 
time period. If any showers do form, the best chance of seeing these 
would be near the WI/Upper MI border Wednesday night. High pressure 
will then build across the area late Thursday into Thursday evening. 
Otherwise, overnight lows will be in the upper 40s to low 50s with 
high temperatures warming into the upper 70s to near 80 Thursday.

Thursday night into Friday: The next low pressure system is expected 
to lift northward through the Plains once again, lifting a warm 
front through much of WI late Thursday night through the day Friday. 
This will lead to another round of showers and Thunderstorms from 
Friday morning through late Friday afternoon. If the clouds clear 
from early day showers and thunderstorms, then stronger afternoon 
thunderstorms will become increasingly likely as instability 
increases and directional/speed shear values also increase. In 
addition, there will also be some upper-level jet support during the 
late afternoon hours. This will be behind the departing warm front 
and ahead of the approaching cold front. Early in the day, it looks 
like a shortwave will slide through the area; however, it looks like 
the afternoon convection would be lacking a mid-level shortwave. 
This may change, which is common as this largely depends on 
convection placement along and ahead of the system within 24 hours 
of the system passing through. Overall details will need to be 
worked out as we get closer to the end of the week, but it will be 
worth keeping an eye on over the next few days. Temps will continue 
to be above normal with afternoon highs running into the upper 70s 
and low 80s with overnight lows only dropping into the upper 40s and 
low 50s.

The rest of the extended: Much of the CWA looks to be between 
systems through much of the upcoming weekend. This would give fairly 
quiet weather for this time period. The next chance of 
rain/thunderstorms would be Sunday night into next Monday. At this 
point, will stick with a consensus of the models, keeping the 
weekend dry with temperatures in the upper 60s to mid 70s. Overnight 
lows expected to be in the upper 40s.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1035 PM CDT Mon May 20 2019

Good flight conditions are expected to last into Tuesday 
afternoon as high pressure slowly departs off to the east. Clouds 
will thicken and lower tomorrow, but ceilings should remain VFR 
until tomorrow evening. The initial surge of precipitation into
the area tomorrow evening will likely weaken as the best forcing
stays to the west.
&&

.HYDROLOGY...
Issued at 242 PM CDT Mon May 20 2019

Area rivers/streams continue to rise due to heavy rainfall from
this past weekend. While most rivers are forecast to remain below
flood stage, additional rainfall later this week will keep the
rivers elevated. In addition, the release of water from dams along
the Wisconsin and Menominee rivers will generate fast flows
downstream. Anyone living near rivers/streams should keep abreast
of the latest weather information and be prepared to seek higher 
ground should any flooding occur.
&&

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

$$

SHORT TERM.....Kallas
LONG TERM......Cooley
AVIATION.......Skowronski
HYDROLOGY......Kallas