Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 230727

Area Forecast Discussion
National Weather Service Marquette MI
327 AM EDT Thu Mar 23 2017

.SHORT TERM...(Today and tonight)
Issued at 326 AM EDT THU MAR 23 2017

Upper air pattern consists of a 500 mb ridge over the plains and a
trough in the western U.S. this morning. There is also a shortwave
over Saskatchewan and Manitoba. The trough will move east into the
central plains on Fri with the area on the top of the upper ridge
through tonight. Weak 850-500 mb q-vector convergence moves across
the area through tonight. Deeper moisture tries to move through this
morning and then returns again tonight.

Complicated forecast with pcpn types for tonight. Looked at some
soundings and they all point to a warm layer aloft over a lower
layer of air that is around freezing. This will mean that most of
the pcpn tonight will be in a rain/freezing rain form. Right now,
not comfortable going with an advisory for freezing rain as the sfc
temperatures continue to be tricky being one or two degrees either
side of freezing. If temperatures are above freezing, there would be
no problem. Below freezing, could see up to 0.25 inch of ice. The
temperatures depend on how much we warm up today and then also
depend tonight on how much we evaporatively cool as the dry air at
the sfc will have to moisten up when pcpn starts. Will continue with
a special weather statement for now and mention the icing potential.
Will go with dry dew points into this afternoon. For this morning,
dry air continues to make a dent on the pcpn headed this way as very
little is hitting the ground in Wisconsin and eastern Minnesota.
Will still keep slight chance pops in for this morning and early
afternoon for this.

.LONG TERM...(Thursday night through Wednesday)
Issued at 358 PM EDT WED MAR 22 2017

Overall confidence in the longer term fcst is lo because the wx into
early next week wl depend on the track/intensity/timing of a closed
lo in the srn branch flow dominating the CONUS, a hi pres passing
thru scentral Canada under a separate nrn branch flow, and the sharp
gradient of mstr btwn these features that wl be near Upr MI thru the
weekend. Because some llvl cold air associated with the hi pres may
bleed into/linger over Upr MI, there could be some mixed pcpn
including freezing ra at times. However, temps into at least early
next week should run aoa normal due mainly to relatively warm
overngt temps. There is likely to be a drying trend next Tue/Wed as
an upr rdg builds over the wrn Great Lks, but there is uncertainty
as to how much cold air wl return on the srn flank of accompanyin hi
pres bldg into nw Ontario.

Thu ngt into Fri ngt...As a closed lo over the srn Rockies embedded
in the srn branch flow dominating the CONUS shifts slowly toward the
mid MS River Valley, guidance indicates an area of pcpn wl dvlp on
Thu ngt over Upr MI to the n of its accompanying warm fnt that wl
extend into the Lower Lks. There remain some sgnft differences as to
how far n the main, most persistent waa/mid lvl fgen pcpn band wl
drift on Thu ngt into Fri as well as the thermal profile/ptype/
impact of llvl evaporative cooling and then on how quickly expanding
sfc hi pres over scentral Canada under the large scale subsidence
behind the passing nrn branch shrtwv wl advect drier air into the
Upr Lks and push this pcpn band to the s on Fri/Fri ngt. Since h85
temps are fcst to rise above 0C over the area and lingering llvl dry
air wl allow for evaporative cooling on Thu ngt that allows for sub
freezing near sfc temps under the elevated warm lyr, there is the
potential for freezing ra/ice accums then before diminished
evaporative cooling with llvl moistening on Fri allows the pcpn to
change to mainly ra.  Considering model qpf, there appears to be a
potential for 0.10 to 0.20 ice accum on Thu night over the interior
w and central cwa. Opted to issue an SPS to highlight the potential
for this icing. Although the 12Z NAM shows more sgnft pcpn farther
to the n into Fri ngt, the bulk of the recent model runs indicate
the most persistent pcpn into Fri ngt wl occur over the scentral
closer to the area of deeper mstr with more aggressive mid lvl
drying over the nrn tier. Considering the far s placement of the upr
lo and the trend for the axis of h85-7 fgen to drift to the s with
time, the farther s model consensus seems on the right track for
Fri/Fri ngt. But Upslope ene winds on the srn flank of hi pres bldg
into nw Ontario ahead of a bldg nrn branch upr rdg axis over
scentral Canada may allow some lgt pcpn to linger a bit longer over
the hier terrain of the ncentral.

Sat into Mon...There remain sgnft differences as to how quickly and
far to the n the srn branch closed lo wl lift thru the weekend. In
general, the medium range guidance has trended toward a farther n
drift into Lower MI, which would allow a gradual return of deeper
mstr and expansion of pops to the n over Upr MI as the drying
influence of the Ontario hi pres diminishes with its shift into
Quebec. Since h85 temps wl be over 0C, accompanying pcpn should be
mainly liquid. The question remains as to how much and how long
colder/drier near sfc air associated with the departing sfc hi pres
wl linger acrs the area that could allow for some freezing ra.

Extended...As an upr rdg blds over the wrn Great Lks on Tue/Wed, the
longer range guidance indicates bldg hi pres in nw Ontario wl expand
over the wrn Great Lks and bring a drying trend to Upr MI. But there
are sgnft differences as to how much cold air wl spill into the area.

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1220 AM EDT THU MAR 23 2017

Mainly VFR ceilings and visibilities are expected through Thursday.
Mid and high clouds will spread from west to east overnight with
winds becoming southerly. There is the potential for a brief band of
snow showers moving through KIWD that could bring cigs to near MVFR
though confidence is limited as the dry low level air in place
should reduce the pcpn intensity. A larger area of rain will move in
Thursday evening as srly low lvl flow increases. This should drop
cigs into the MVFR and possibly to IFR by late evening. Evaporative
cooling should also be strong enough for the rain to change to fzra
at KSAW.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 326 AM EDT THU MAR 23 2017

Expect s winds as hi as 30 kts, with a few gale force gusts to 35
kts possible, on Thu evening over the east half of Lake Superior to
diminish on Thu night thru Fri as a flatter pres gradient dominates.
Expect ne veering e winds to increase up to 25 to perhaps 30 kts on
Fri night into Sun under the tightening pres gradient between hi
pres passing from Ontario into Quebec and lo pres in the lower Great
Lakes. The strongest winds are most likely over western Lake
Superior, where the lake topography will enhance the ene flow. As
these features weaken and exit to the e, winds by Mon will diminish.

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


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