Area Forecast Discussion

FXUS63 KMQT 280522

Area Forecast Discussion
National Weather Service Marquette MI
122 AM EDT Thu May 28 2020

.SHORT TERM...(This evening through Thursday)
Issued at 339 PM EDT WED MAY 27 2020

Hot and humid day across the UP as clear skies across the central 
are starting to show some convection across N Marquette County. 
Ongoing -SHRA across the western shores of the UP remains as -SHRA 
across the eastern central portions of the UP are starting to move 
offshore along the PRNL to Grand Marais. CAMs weren't analyzing 
thunderstorm development across the central this earlier, but 
suspect they also weren't anticipating temperatures to climb into 
upper 80s either. A few cells that have moved over the lake did show 
some signs of melting hail as they pulsed up and then back down 
after moving over the colder water.

Heading into this evening and tonight, expecting more -TSRA 
development across the central as daytime heating and increased sfc 
moisture continues. CAMs suggest broad brush convection to begin 
across the central portions of the UP over the next few hours. 
Latest SPC mesoanalysis suggest 1500-2500 J/kg of CAPE and that will 
linger into the early evening hours as sfc heating continues under 
partly sunny skies. Low-level lapse rates are certainly conducive 
for convection sitting between 7-8C/km per RAP analysis, but 
thankfully wind shear threat continues to remain low with bulk shear 
remaining blo 30kts. As a cold front approaches tonight, models 
suggest rain and thunderstorms to develop along its deformation 
axis. There is some uncertainty as to where exactly this sets up, 
but WPC does have portions of central UP and along Lake Mi shoreline 
in a slight chance for excessive rainfall. Looking at storm motion 
vectors and CAMs, storm motion appears to be along the same axis 
that thunderstorms develop. Mean storm winds will also be on the 
lighter side, near 20 to 25 kts, which will enhance the chance for 
training thunderstorms. Thankfully the trend with the 12Z guidance 
was slightly more to the SE, which puts the main axis of precip over 
Lake MI tomorrow morning. Overall, with PWATs almost 1.5 inches at 
GRB this AM, that is well above the 90th percentile. Latest RAP run 
suggests 1.75 inches of PWAT moving over the central portions of the 
UP tonight. With that, have increased the QPF this evening through 
tomorrow morning, with a broad stroke of a half an inch across the 
central and east, with pockets upwards of an inch. Wherever 
thunderstorms develop and train over, there is certainly the 
possibility that some places exceed the 1to 1.5 inch mark or more.

By noonish tomorrow, models suggest the bulk of the convection to be 
across Lake MI, with ongoing trailing stratiform from Marquette 
County eastward. There is plenty of uncertainty in the CAMs and they 
struggled the past day or two analyzing any precip that developed 
across the central. For now, kept the chance PoPs to go along with 
the model spread, but certainly possible that precip ends up further 
eastward if the frontal axis shifts east.

.LONG TERM...(Thursday night through Wednesday)
Issued at 246 PM EDT WED MAY 27 2020

Upper air pattern will consist of a 500 mb shortwave over the upper 
Great Lakes 00z Fri with another over the mid Mississippi valley. 
The two shortwaves combine on Fri over the lower Great Lakes with 
more troughing dropping in to form a deeper trough over the eastern 
U.S. on Sat. This will slow the advancement east of the pcpn a bit 
Thu night and then quieter and drier air moves in for Fri and Fri 
night. Overall, did not make too many changes to the going forecast. 

In the extended, the GFS and ECMWF show a 500 mb ridge over the 
Rockies 12z Sun with a trough over the ern half of the U.S. The 
ridge moves into the plains 12z Mon with the trough on the east 
coast. By 12z Wed, the trough has moved off the east coast with the 
trough still in the plains. The ridge then moves into the upper 
Great Lakes 12z Wed. Warming trend will occur this forecast period 
with temperatures going back to above normal by mid week. Manual 
progs show a sfc front getting hung up over the area on Tue into Wed.

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 122 AM EDT THU MAY 28 2020

Scattered showers are affecting many of the terminals late this 
evening. No immediate concerns for thunderstorms at the terminals, 
although KSAW might see an isolated t-storm in the vicinity from 06-
09Z into the overnight. Did not include vicinity mention as coverage 
of t-storms should be pretty isolated. Conditions at KIWD have 
improved to VFR and should remain that way through period as showers 
should stay east. Lingering low-level moisture and lighter upslope 
winds may bring fog to CMX tonight, resulting in mainly MVFR to IFR 
conditions, then expect improving conditions to VFR by midday Thu. 
KSAW will lower to MVFR to IFR overnight as showers fill in ahead of 
a trough, and as mentioned, thunder not out of question. As showers 
shift east of KSAW late Thursday morning with movement of 
trough/frontal boundary, conditions will gradually improve to VFR by 
mid to late afternoon as drier air works in from the west.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 339 PM EDT WED MAY 27 2020

Winds will remain generally blo 25 knots through the extended 
forecast. Fog, dense at times, will linger through tonight, before 
diminishing from west to east behind a cold front tomorrow morning. 
Thunderstorms and rain will develop and pass over the eastern half 
of Lake Superior tonight into tomorrow morning, which could bring a 
few gusts to near 30 knots.

Upper Michigan...
Lake Superior...
Lake Michigan...
  Dense Fog Advisory until 11 AM EDT this morning for LMZ248-250.