Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 190833
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
433 AM EDT Thu Apr 19 2018

.SHORT TERM...(This evening through Thursday)
Issued at 309 PM EDT WED APR 18 2018

Clouds have been quick to clear this afternoon as a very dry airmass
advects into the area. Gusty winds of 15-25 kts have developed in
response to the pressure gradient from the high/low in western
Ontario/southern Great Lakes. Winds are expected to relax this evening
except across the far east as temperatures drop to the 20s. A shallow
layer of clouds is expected to redevelop along the north central Lake
Superior shore this evening but the dry low-level airmass, relative
shallow depth of the cloud deck, and little mechanical mixing atop the
cloud top should prevent any freezing drizzle.

Thursday looks quite splendid with mostly sunny skies and highs in the
40s top near 50 along the Wisconsin border.

.LONG TERM...(Friday through Wednesday)
Issued at 433 AM EDT THU APR 19 2018

A quiet period of weather is still expected thru early next week
with temperatures returning to more typical mid/late Apr values.
Obviously, the quiet weather will be ideal as we don`t need to add
rain to the snowpack which will be melting down under warmer
conditions and high spring sun angle. Building positive height
anomaly across s central Canada and Hudson Bay will force the next
shortwave trof now moving onshore in CA way to the s across the
Lower Mississippi Valley/SE States late weekend/early next week. A
couple of shortwaves will then track eastward in the vcnty of the
U.S./Canada border during the first half of next week. The first may
not generate any shra for Upper MI as it passes well to the n. More
vigorous second wave should pose a decent potential of rain then
rain/snow Tue into Wed. As for temps, warming trend will occur thru
the weekend as development of positive height anomalies across s
central Canada ensures no late season cold air to the n. Temps will
rise to around normal or slightly above normal as snowcover should
not really inhibit warming given the high sun angle working on the
forested Upper MI landscape on mostly sunny days. A cool down is
expected for the middle of next week as trof passes.

As was the case yesterday, there are no major weather concerns for
this fcst cycle. Mean mid/upper level ridging over s central Canada
to Hudson Bay will support sfc high pres over the Great Lakes region
Fri thru Sun, resulting in dry weather. The GFS still spits out some
pcpn Fri aftn and Sat aftn in the lake breeze convergence zone
central, a result of too much low-level moisture from melting snow.
This has been a bias seen in the model in recent weeks. Outside of
some high clouds at times, generally sunny days and clear nights are
expected thru Sun, a fairly typical spring time scenario for Upper
MI. Winds will be on the light side thru the weekend, especially
Fri/Sat, with high pres over the Great Lakes region and meso highs
setting up each aftn over the waters, particularly Fri/Sat, leading
to the usual chill near the lakes each aftn (temps in the 30s). Away
from lake cooling, high temps will be in the 50s Fri thru Sun,
though some locations will likely top 60F Sat/Sun. Best chc of
seeing more widespread max temps at or above 60F will be on Mon
ahead of approaching cold front. Good radiational cooling nights
will be coming up with tonight being the best. Fri night/Sat night
will still feature good nighttime cooling though models suggest
thicker high clouds will pass acros the area Fri night. Favored the
bias corrected global CMC for mins as it is typically a superior
performer on radiational cooling nights. Dry air mass over the area
and generally little cloud cover will support large diurnal temp
swings, especially while snow cover is still consistent across the
landscape to allow sharp nighttime temp falls. Interior mins should
tumble back to the low/mid 20s Fri night/Sat night. Incorporated
lower dwpt guidance into the fcst to adjust dwpts down as some of
the raw model fcsts, GFS in particular, included in the blended
guidance are raising sfc dwpts too much with the melting snow.

Cold front associated with first shortwave will slowly move across
the fcst area Mon night thru Tue as it slows down in response to
second shortwave approaching. At this point, it appears the front
will initially arrive without any pcpn. There is plenty of
uncertainty with the second, more vigorous shortwave arriving
midweek. However, at least for the 00z runs, the GFS/CMC/ECMWF are
surprisingly similar depicting a mid-level low closing off as the
wave moves across the western Great Lakes, a scenario that could
lead to rain transitioning to some accumulating snowfall for at
least parts of the area. Despite the 00z run agreement, there are
not a whole lot of ensembles supporting that idea at the moment.
Will be something to monitor. Significant rainfall should not be a
concern with this system as flow behind southern stream wave moving
from the Lower Mississippi Valley to the SE States will prevent Gulf
moisture return to this northern system.
&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 130 AM EDT THU APR 19 2018

Primary concern for the overnight period will be to closely monitor
IWD for possible fog formation, although if it does come to
fruition, should teeter in the upper-end of the MVFR category.
Otherwise, VFR looks to prevail throughout the rest of the TAF
period. Additional considerations for gusty NNE becoming NNW winds
to continue during the overnight period well into the daylight hours
on Thursday for SAW before surface ridging moving in from the west
helps to settle the winds down area-wide.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 309 PM EDT WED APR 18 2018

Winds will remain between 20 to 30 knots through Thursday morning.
A few gale force gusts to 35 knots can`t be ruled out across the
eastern half of Lake Superior this afternoon. Winds will then
relax below 20 knots from west to east on Thursday, remaining
relatively calm through the weekend.
&&

.HYDROLOGY...
Issued at 433 AM EDT THU APR 19 2018

Snowpack will be melting thru at least early next week under warming
which will push temps to around normal or even slightly above
normal. Mostly sunny days thru the weekend will strongly aid the
melting. With nighttime temps falling blo freezing and dewpoints
likely remaining low, only a gradual increase in melting/runoff
should occur. Early next week, min temps may not fall blo freezing
for a night or two, increasing runoff potential, though dewpoints
will likely remain low, keeping melting of snow slower than would
otherwise occur. The addition of notable rainfall is the biggest
concern to increase flooding potential. Fortunately, there will be
no pcpn thru the weekend, and pcpn which occurs Tue/Wed should be on
the light side as a cold front passes. Temporary cool down following
the frontal passage will then slow down the ongoing snow melt.
Overall, these conditions don`t suggest any significant concerns
with the snow melt over the next 7 days. While melting will likely
be relatively controlled given the forecast, rivers will begin to
respond this weekend and minor flooding is quite possible at some
point down the road on the usual rivers that experience spring
flooding.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...Borchardt
LONG TERM...Rolfson
AVIATION...lg
MARINE...Borchardt
HYDROLOGY...Rolfson



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