Area Forecast Discussion
Issued by NWS Marquette, MI

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356
FXUS63 KMQT 191947
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
347 PM EDT Thu Apr 19 2018

.SHORT TERM...(This evening through Friday)
Issued at 345 PM EDT THU APR 19 2018

Thanks to the abundance of coniferous trees across Upper
Michigan, temperatures today across the central and interior U.P.
have jumped to the upper 40s and lower 50s. Dew points have
fallen more than expected today even with melting/sublimating
snow, contributing to the higher temperatures. Wind primarily off
Lake Superior have kept temperatures in the upper 30s to lower 40s
across the west and east. With clear skies, low dew points, and
weakening winds overnight, low temperatures are expected to
plummet into the teens across much of the area with the coldest
temperatures expected across the interior west. Relied heavily on
the bias-corrected Canadian tonight for overnight lows as it did
very well last night.

There is some concern for the development of a very shallow (<100
ft) layer of patchy freezing fog toward sunrise, especially across
the central interior. The very dry airmass in place should limit
both the vertical and horizontal spatial extents of any fog
development, but conditions will have to be monitored closely
tonight to see just how fast temperatures drop off.

Highs on Friday were upped a few degrees from the previous forecast
package based on expected abundant sunshine and very little wind.
Overall, Friday looks very pleasant.

.LONG TERM...(Friday night through Thursday)
Issued at 332 PM 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 for a more gradual runoff
of the melting snowpack under warmer conditions and high spring sun
angle. Building positive height anomaly across s central Canada and
Hudson Bay will force the next shortwave trough 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 vicinity of the U.S./Canada border during the first
half of next week. The first may not generate any showers for Upper
MI as it passes well to the n. A more vigorous second wave should
pose a decent potential of rain late Tue then rain/snow Tue night
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 the vigorous trough 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 generates 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, allowing for the generation of lake breezes in the
afternoon leading to the usual afternoon chill near the lakeshores
with temps likely falling into 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 with waa sw flow 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 across the area Fri night. Favored the bias corrected global
CMC for mins as it is typically performs better 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 for
sharp nighttime temp falls. Interior mins should tumble back to the
low/mid 20s Fri night/Sat night. Will utilize lower model dewpoint
guidance into the fcst (especially daytime) as some of the raw model
fcsts, GFS in particular, included in the blended guidance are
raising sfc dewpoints 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 with little, if any, pcpn. Models continue to
show differences in strength/evolution of the second, more vigorous
shortwave arriving midweek, with the 12z GFS showing a more open and
progressive wave while the 12z ECMWF and Canadian continuing to
depict a developing closed mid-level low as the wave moves across
the western Great Lakes. Either way these models appear to be
trending toward weaker forcing with this second wave and thus more
scattered pcpn. Expect scattered light rain showers late Tue
transitioning to a mix of light rain/snow showers Tue night into
Wed. Significant rainfall should not be a concern with this system
as nw flow behind southern stream wave moving from the Lower
Mississippi Valley to the SE States will block Gulf moisture return
into this northern system.
&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 121 PM EDT THU APR 19 2018

VFR conditions will continue at all TAF sites through the entire
period. Winds at KSAW may waver between 330 and 030 this afternoon
progresses owing to channel flow around the topography to the
west and a lake breeze currently stalled along the Lake Superior
shoreline. However, winds will weaken and back at all sites just
after sunset. Finally, a very shallow layer of patchy fog may
develop near KIWD and KSAW toward sunrise but confidence is too
low to include in the TAFs at this time.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 220 PM EDT THU APR 19 2018

Gusts of 20-25 kts this afternoon will diminish overnight and remain
below 20 kts through the rest of the forecast period.
&&

.HYDROLOGY...
Issued at 332 PM 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...Voss
AVIATION...Borchardt
MARINE...Borchardt
HYDROLOGY...Voss



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