Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 281746
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
146 PM EDT Fri Apr 28 2017

.SHORT TERM...(Today and tonight)
Issued at 405 AM EDT FRI APR 28 2017

Water vapor imagery shows deeper wrap around moisture, associated
with the system that lifted north across the area yesterday,
continuing to slowly lift across southern portions of Canada this
morning. Much of the precipitation associated with this system has
come to an end, with the exception off the Keeweenaw Peninsula where
onshore, upslope flow and cold air advection have allowed light snow
to linger through the morning hours.

Expect the light snow to linger across the Keweenaw Peninsula
through the morning hours before gradually tapering off as drier air
begins to advect southeast across the area, along with increasing
upper-level subsidence as the left-rear quadrant of an upper-level
jet will lift across the area. Elsewhere, expect clouds to linger
through much of the day. Towards the afternoon hours, we could see a
few peeks of sunshine as clouds should become more broken, opposed
to overcast. With the pocket of cold air still lingering overhead,
expect winds to get a bit gusty this afternoon given the steep low-
level lapse rates and 20-30 knot 925-850mb flow. High temperatures
will be tricky today given cloud cover, cold air advection, and
downsloping westerly winds across portions of the area. The warmest
locations look to be across the south central portions of Upper
Michigan, where downsloping flow will aid in adiabatic warming.
Tonight, cloud cover will diminish into the early morning hours with
lows dropping below freezing.

.LONG TERM...(Saturday through Thursday)
Issued at 436 AM EDT FRI APR 28 2017

The active pattern that has brought frequent bouts of pcpn to the
fcst area over the last couple of weeks will continue into early
next week. Main focus during the long term will be on the system
organizing over the southern Rockies this weekend. This will become
a vigorous spring storm system as it lifts into the Upper Great
Lakes early next week, bringing another round of healthy pcpn,
including some wintry pcpn. Once this system passes, a large scale
pattern change is in the offing. Ridge/positive height anomaly
currently off the W Coast will build into the western CONUS by the
middle of next week, shifting the recent mean Rockies/Plains trof
eastward and ending the train of ne tracking shortwaves across the
central CONUS. However, as the ridge shifts e, one more shortwave
will round it, dropping into the Southern Plains/Lower Mississippi
Valley during the middle of next week. While progession of the large
scale pattern should keep the storm system that this wave spins up
(another big pcpn producer) well se and e of the Upper Lakes late
next week, it will be something to monitor. If the upstream ridge is
sharper, leading to a more strongly digging shortwave, the
progression of the large scale trof will be held up more than
reflected by current operational model guidance and could result in
another Great Lakes storm system. As for temps, blo normal temps
will prevail over the next 7 days. Departures from normal for max
temps will be most notable with a day or two 15-20 degrees blo
normal. Looking farther ahead, CFSv2 ensemble mean fcsts point
toward overall blo normal temps thru mid May. That doesn`t mean
there won`t be some warm days, but rather that the pattern shouldn`t
support any longer periods of above normal temps.

Beginning Sat, dry air mass associated with high pres building over
northern Ontario will lead to a dry day with sunshine becoming
filtered by some increase in high clouds. A fairly steady wind off
Lake Superior will keep it cool across the n. Lakeside locations
probably won`t get out of the lower 40s. Interior s central should
reach the lwr 50s.

Attention then turns to the shortwave exiting the the southern
Rockies Sat evening and then lifting ne toward the Upper Great
Lakes. Over the last few days, model trends from the GFS/ECMWF/CMC
have shifted the track of this storm system to the nw. Given the
strong ridge just off the E Coast (500mb height anomalies around
200m), it`s unlikely that future model runs will show any notable
shift of the storm track to the se. As a result of the nw shift of
the storm track, only the far western fcst area really has any
potential of seeing a significant snowfall from this system, but
that potential is very low.

Initially Sat night/Sun, deepening mid level low will lift ne to
eastern KS by Sun evening with sfc low reaching nw MO. Weaker
shortwaves lifting nne ahead of this feature will aid deepening
southerly flow and the transport of abundant moisture northward into
the Great Lakes. Models are in very good agreement that these waves
and strong moisture transport will support periods of heavy rainfall
lifting from the Plains to Lower MI Sat night/Sun. This pcpn may
brush mainly the se fcst area. Main pcpn event for Upper MI will
hold off until the mid-level low moves closer Sun night/Mon.
Vigorous deep layer forcing per q-vectors combined with strong
isentropic ascent/moisture transport will likely support a band of
mdt/hvy pcpn swinging n across the area late Sun night/Mon morning.
In addition, with mid-level dry slot surging nne, not out of the
question that there could be a few rumbles of thunder on the
backside of the mdt/hvy pcpn band as it lifts across the area. Pcpn
may begin as snow over the n central, but all operational model
guidance bring enough warming to keep any snow short-lived. Over the
far w, GFS and CMC still maintain just enough cold air so that ptype
may stay snow for much, if not all, of the event. The 00z CMC has
shown a warming trend from the 12z run. Meanwhile, the last 3 of
runs of the ECMWF indicate ptype during the push of mdt/hvy pcpn
will be just rain across the fcst area, not changing to snow until
the mid-level low arrives when pcpn will be light. While there are a
few GFS ensembles that are colder, supporting mainly snow for the w,
believe the warmer solutions are probably on the right track.
Furthermore, given the strong ridge/positive height anomaly near the
E Coast, it seems very unlikely that we`ll see a se shift of the
fcst storm track and a colder solution for Upper MI in upcoming
model runs. So, for now, fcst will continue to include some snow
over the w Sun night, but little/no accumulation. As the mid-level
low moves across and then ne of the Upper Lakes, expect -sn to
spread across the area Mon night/Tue, especially the w and n. Some
snow accumulations should occur, with 1-2 perhaps 3 inches possible
in the high terrain of the w and nw where upsloping will aid
snowfall. Probably won`t be quite cold enough for lake enhancement.

Lingering light pcpn should end Tue night. Attention then shifts to
the progression of the ridge into the western CONUS and the
shortwave that will drop down its front side into the southern
Plains/Lower Mississippi Valley. While the 00z GFS/ECMWF/CMC show
enough progression of the large scale pattern to keep this wave and
resulting storm system that it spins up well to the se of here late
week, it is noted that there are some CMC/GFS ensembles that become
more amplifed farther w, resulting in another Great Lakes storm
system, one that could include snow for parts of Upper MI. At the
moment, this is a very low probability given bulk of guidance is
well se, but it will be something to monitor over the next several
days. For now, fcst for Wed-Fri will reflect mainly dry conditions
with temps moderating back closer to normal.
&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 145 PM EDT FRI APR 28 2017

MVFR ceilings will continue to improve early this afternoon into the
VFR category. Once the TAF sites go to VFR, that should be the going
forecast through the remainder of the TAF period. Gusty winds this
afternoon will steadily decrease through the night into Saturday.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 405 AM EDT FRI APR 28 2017

West winds of 20 to 30 knots are expected today. Locations west and
north of the Keeweenaw Peninsula will see the strongest winds as
west winds back slightly west-southwest, allowing for flow to
accelerate as it gets funneled along the coastline. By Saturday
morning, winds will become northerly and decrease to 10 to 15 knots
as high pressure moves across the region. By Sunday, the pressure
gradient will start to increase once again as winds become east-
northeasterly 15 to 25 knots. Sunday night through Monday, east-
northeast flow will increase to gales of 35 to 40 knots across the
west and central portions of Lake Superior. As low pressure tracks
northeast across the Upper Great Lakes, winds will back to the north
20 to 30 knots into Tuesday morning. Wednesday and Thursday, winds
will be less than 20 knots as high pressure builds across the
region.
&&

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

$$

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



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