Area Forecast Discussion
Issued by NWS Marquette, MI

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952
FXUS63 KMQT 220555 CCA
AFDMQT

Area Forecast Discussion...CORRECTED
National Weather Service Marquette MI
1255 AM EST Thu Feb 22 2018

.SHORT TERM...(This evening through Thursday)
Issued at 239 PM EST WED FEB 21 2018

Overall, quiet weather has begun to settled in for the
next 24 hours across Upper Michigan. Lingering light lake effect
snow showers across the west to northwest wind snow belts has
gradually diminished this afternoon as surface ridging began to lift
northeast. Ample sunshine was observed across much of western and
central Upper Michigan, where temperatures quickly rebounded into
the upper teens and 20s through the afternoon hours.

The main forecast concern over the next 24 hours are temperatures.
Tonight, surface ridging will continue to track northeast across
Upper Michigan. The resulting drier air mass, clear skies, and light
winds will give way to ample radiational cooling across the area.
Not terribly impressed with how guidance seems to be handling the
potential for colder temperatures tonight, so did make manual
adjustments to lower temperatures down below zero across the interior
west and central. Elsewhere, temperatures should easily drop into
the single digits. Thankfully, winds will be light tonight so there
will be no wind chill concerns. Thursday, warm air advection will
begin to gradually lift northward with thickening cloud cover during
the afternoon. Temperatures will warm a few more degrees compared to
today as a result, with highs climbing into the upper 20s to lower
30s. Snow chances will hold off until Thursday night, when the next
system is progged to track across the region - see the latest long
term discussion for further details.

.LONG TERM...(Thursday night through Wednesday)
Issued at 408 PM EST WED FEB 21 2018

In contrast to the lack of synoptic pcpn events for Upper MI so far
this winter, the pattern thru next week will be active with 2 pcpn
events in the next 7 days and potentially another event late next
week. The first one Thu night/Fri should produce a light to mdt
snowfall. The second one over the weekend is looking much more
important and could be a significant snow producer for portions of
Upper MI, but it will probably also include mixed ptypes and maybe
even rain for a time in other parts of Upper MI. The active pattern
for at least the next 7-10 days will be the result of persistent
western CONUS troffing. While a very strong ridge currently exists
downstream, centered just off the E Coast (500mb height anomalies
are around 400m along the New England coast), it will deamplify next
week. Then, with the NAO trending toward a fairly strong negative
phase, the eastern ridge should be replaced with troffing later next
week and would suggest a trend toward a more suppressed storm track
with time for shortwaves ejecting from the western trof. As for
temps, with a mean western trof dominating, temps thru next week
will be running near normal or above normal each day with above
normal likely on the majority of days. Farther down the line, the
development of a negative NAO normally favors a cold pattern for the
Upper Lakes. While temp signals from guidance still don`t really
indicate a shift to blo normal, would expect a trend toward a period
of colder weather in early Mar.

Beginning Thu night into Fri...a shortwave will shear ne into the
Upper Lakes, bringing a period of waa/isentropic ascent. Mixing
ratios up to around 3g/kg are avbl in the 700-750mb layer,
suggesting potential of 3-5in of snowfall for 6-9hrs of main ascent.
Snow ratios will be on the lower side with relatively narrow DGZ at
or above 10kft. So probably looking at "wetter" snow accumulation on
the order of 1-3in to locally 4 across the area with the higher
amounts over the w. A period of transient low-mid level fgen,
affecting mainly western Upper MI, may boost totals a little more
than reflected in this fcst. Snow will develop sw to ne Thu night
then diminish and/or end sw to ne Fri morning/early aftn. The snow
may mix with or change to a little -fzdz in some areas as the pcpn
diminishes/ends on Fri. In the end, may need advy headline for at
least western Upper MI. Probably won`t be cold enough for any LES
behind this wave as 850mb temps only fall back to around
-10C. So, a quiet period of weather will follow Fri night/Sat.

Sat night/Sun...attention turns to the next shortwave ejecting from
the mean western trof. Medium range models show this shortwave being
stronger than its predecessor. While the GFS has maintained its
position as a strong solution for 6 runs and as the strongest of the
medium range models, the GEM and ECMWF are trending stronger. GFS
runs have been consistent in spinning up a 980s mb or lower sfc low
with a hvy snow band to the nw of the low track as it lifts into the
Great Lakes. All of the GFS ensembles are similarly strong or
stronger than the operational run. They also support the operational
sfc low track ne across central Upper MI, but there are more leaning
a bit farther w with the track than farther e. At a minimum, this
would shift hvy snow risk to far western Upper MI and points w and
would shift potential ptype transition to just rain westward into
portions of central Upper MI. The GEM offers a less wrapped
low/colder solution yielding ptype as more snow, but not as much
QPF. There has been a clear trend in the GEM ensembles for more
members to show a stronger sfc low and with tracks clustered thru
central Upper MI, similar to the GFS. ECMWF has not been avbl in the
NWS system for a few runs, so don`t have a good handle on its
temp/pcpn trends. What is avbl elsewhere shows a definite stronger
trend with the 12z run showing a 982mb sfc low over far se Lake
Superior at 12z Sun. Given the strength of the eastern ridge, a
western sfc low track solution more inline with the GFS is probably
on the right track, and wouldn`t be surprised to see an additional
slight westward shift in later model runs. So at this point, far
western Upper MI has best potential of getting into the hvy snow
band w of the low track. To the e, much of rest of the area will
probably see snow becoming a mix, and then at least the eastern fcst
area has the potential to change to all rain. If the low is weaker
and not as wrapped up, there would be a better chc for pcpn to
remain as all snow over more the area. Still looks like Sat
night/Sun morning will be the main time period for pcpn.

Should be cold enough for a short period of some lake enhanced snow
in the wake of the system, but once synoptic forcing exits, temps
will be marginal at best for pure LES. Expect a quieter period into
mid week. Potential late week system will depend on the upper flow
adjustment over N America in response to the strong negative NAO
developing. Response should be to shift storm track farther s from
the previous systems.
&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1250 AM EST THU FEB 22 2018

VFR ceilings and visibilities are will prevail through about 00Z
Thursday with light winds.  As a clipper system approaches from the
southwest, MVFR conditions are expected at KIWD and KCMX by about
05Z in accordance with lowered ceilings and visibilities.  There is
somewhat low confidence that MVFR conditions will be met before 05Z
Thursday depending on the speed of the incoming system, but exact
timing will be refined in later updates.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 239 PM EST WED FEB 21 2018

20 to 30 knot winds over Lake Superior will relax to less than 20
knots by Thursday morning as high pressure lifts across the region.
Expect winds to remain below 20 knots through much of Saturday. A
strengthening low pressure system is progged to track across the
Upper Great Lakes later this weekend; therefore, expect winds to
ramp up to between 20 to 30 knots.
&&

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

$$

SHORT TERM...Ritzman
LONG TERM...Rolfson
AVIATION...Borchardt
MARINE...Ritzman



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