Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 241803

Area Forecast Discussion
National Weather Service Marquette MI
203 PM EDT Tue Apr 24 2018

.SHORT TERM...(Today and tonight)
Issued at 459 AM EDT TUE APR 24 2018

WV imagery and RAP analysis indicated a split flow pattern with an
upstream northern stream shortwave trough from nw Ontario into ne
North Dakota and a compact mid level low just to the south over wrn
South Dakota. At the surface, a cold front extended from ne lake
Superior through the Keweenaw Peninsula into nw WI. Mostly clear
skies prevailed across Upper Michigan with only some high clouds
over the se. Clouds were thickening over nw MN ahead of the shrtwv,
but no pcpn was observed.

Today, expect clouds to increase as the shrtwv approaches, per
upstream satellite trends. Although moderate 850-700 mb fgen slides
se into Upper Michigan this afternoon, and exits the se by late this
evening, with only limited moisture availability and llittle/no
inflow, only slight chance POPs at best are expected. Since the
low levels remain relatively dry, mainly just a few sprinkles
would be expected. Northerly flow CAA will bring cooler air into
the area with highs only in the 40s north near Lake Superior to
the upper 50s south.

Tonight, models suggest that skies will clear from west to east
during the evening with drier air moving in. However, upslope
northerly flow aided by some lake moisture will support increasing
clouds north central late.

.LONG TERM...(Wednesday through Monday)
Issued at 432 AM EDT TUE APR 24 2018

Roller coaster for temperatures is expected into next week. Coldest
day will be on Fri behind cold front that moves through Thu night.
Warmest days will be Sun and Mon as upper level troughing that moves
overhead Fri-Sat is replaced by sharp ridging and very warm temps
aloft. Though could see some light rain showers changing to rain and
snow showers Thu night into Fri, heavier rain and maybe some
thunderstorms will not affect the area until next week.

Upper troughing that brings cold front through today will be heading
east of Upper Michigan daybreak Wed. High pressure builds in
bringing dry conditions. NW gradient winds result in highs on Wed
staying near 40F near Lk Superior central and east. Away from
lake moderation off Lk Superior, expect temps to push well into
the 50s toward the Wisconsin state line. High sliding east of
Upper Michigan Wed night into Thu will lead to brief warming
again. Highs on Thu ahead of approaching cold front should reach
60F over most of central and east away from Lk Michigan. Readings
could rise well into the mid to upper 60s south central. Cold
front sweeps through Thu night and should be exiting eastern Upper
Michigan daybreak Fri. Strongest forcing with the front should
stay north of Lk Superior. GFS and GEFS indicate likely showers
with total qpf to a 0.25 inch. Other models show lighter qpf with
most areas seeing brief push of showers dropping maybe 0.10 inch
of qpf. Enough cold air as front exits that precip could end as a
little light snow with minimal accumulations. As mentioned
previously, N to NW winds may get gusty in wake of the front.
Could see gusts near Lk Superior east of Marqeuette exceeding 30
mph Thu night. Winds may also get gusty on northern Lk Michigan
behind the cold front. May be looking at marine small craft
advisories for both areas due to the winds and building waves.

Trend the models have now latched onto compared to last couple
days output is secondary more compact and focused shortwave
trough crossing Upper Michigan on Fri in clipper fashion from
northwest to southeast. Current forecast only has slight chances,
but these certainly may need to be increased as the week goes on.
Ptype should stay mainly rain with adequate sfc-H85 warm layer
present as the system works through. Cold air lingers into Sat
then a significant warm up is still in store starting Sun aftn.
Temps on Sun could reach the 60s to near 70F west with climbing
temps aloft and sfc SW gradient winds. Warm up is further magnified
on Mon with strong sfc flow sfc-H85 and H85 temps rising up to
+13c. Deep mixing with this warm air aloft will result in max
temps possibly cracking the 80F mark for the first time this
spring through current forecast is close by in the mid to upper
70s. Coolest temps will be near Lk Michigan as is typical for
Spring warm ups with SW winds. Currently model dwpnts indicate
upper 30s to mid 40s which seems pretty reasonable. And then
there is the matter of a possible rain event with the ECMWF
hinting at thunderstorms with total qpf by 12z Wed over 1 inch.
GFS not as bullish, but based on GEFS probabilities, could see at
least a half inch of qpf starting late Tue. Main impact of the
warm temps and rain will be on ongoing snow melt and runoff into
area rivers. Will be something to keep eye on for sure.

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 155 PM EDT TUE APR 24 2018

Northerly winds will prevail into Wed behind a cold frontal
passage. Although there is a slight chance of showers this
afternoon, mainly just mid clouds are expected with a low
confidence of pcpn, especially that would restrict vsby or lower
cigs. Persistent upslope flow of colder air into north central
Upper Michigan late tonight into Wed morning is expected to bring
a period of low-end VFR to high-end MVFR cigs to KSAW late in the
forecast period. &&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 459 AM EDT TUE APR 24 2018

Northwest winds will increase to around 25 knots over central and
eastern Lake Superior late this afternoon into this evening and then
diminish overnight. Wednesday through Thursday, winds are expected
to remain below 20 knots across all of Lake Superior. Winds will
then pick up to 20 to 30 knots Thursday night with the passage of
another cold front.

Issued at 432 AM EDT TUE APR 24 2018

Snowpack continues to melt steadily but runoff/rises on rivers has
been manageable to this point. The melt thus far has been gradual
with most locations losing 2-4 inches of their snowpack each of the
last few days. Some of the big winners from the last storm are
down around 20 inches compared to max snow depths from a week ago.
Now, though the snow depth is going down steadily, the liquid
water in the snowpack (SWE) is only slowly decreasing as evident
by our SWE last couple days (steady around 7.4 inches) and recent
modeled SWE per NOHRSC. Snowmelt should slow in the next 24-48
hours as temps cool, especially at night with below freezing temps
expected. No change in limited heavy precip chances through the
weekend. Still could be some light precip under one-quarter inch
late Thu into Thu night. Starting to look like we will have to
keep eye on conditions by early next week as there are indications
we could be in store for a significant warm up accompanied by
more low-level moisture/higher dwpnts than we have seen recently.
There could even be appreciable rainfall and possible thunder
just by middle of next week. If these conditions do develop and
snowpack left still has a decent SWE lingering, we could see minor
flooding on the usual rivers that experience spring flooding, so
we will continue to monitor.

Upper Michigan...
Lake Superior...
Lake Michigan...


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