Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 220831
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
431 AM EDT Tue May 22 2018

.SHORT TERM...(Today and tonight)
Issued at 431 AM EDT TUE MAY 22 2018

Water vapor imagery and RAP analysis show shortwave that was over
the central Plains 24hrs ago now shearing e across the western Great
Lakes in the more confluent flow regime over the area between a deep
trof over ne Canada and low amplitude ridging from the southern
Plains e into the Atlantic. Very little shra activity remains with
this wave. Only isolated -shra/sprinkles are noted in ne WI.

Not out of the question that there could be a few sprinkles over far
s central Upper MI over the next few hrs. Otherwise, weak nw low to
mid-level flow developing in the wake of the shortwave will advect
drier air into Upper MI today, leading to clearing skies. This will
allow temps to rise well into the 70s in the interior, perhaps
reaching 80F at a few spots. Under a weak gradient wind regime
today, lake breezes will rule the aftn, leading to cooler conditions
lakeside. There is some question as to how far sfc dwpts may fall
this aftn under drying air mass. Utilizing mixing heights, RAP
suggests dwpts will fall most over nw into n central Upper MI. The
NAM is similar, but much more muted with the dwpt drop. The GFS
favors the central and eastern fcst area for a sharp drop in dwpts.
In the end, combined some of the mix down potential from the RAP and
GFS with bias corrected guidance to arrive at aftn dwpts. Result is
min RH falling to 25-30pct over a wide portion of central Upper MI
inland from the Great Lakes. With sustained winds light in the 5-
10mph range at most locations, fire wx concerns will not be further
aggravated today.

Quiet night is on the way tonight under clear skies and calm/near
calm wind. Expect mins in the 40s, though a few of the traditional
cold spots over the interior e may slip blo 40F. Some guidance is
suggestive of at least patchy fog development tonight. Given the dry
conditions that have dominated in recent weeks and the drying
expected this aftn under building mixed layer, fog seems unlikely
tonight unless the expected drying of the boundary layer fails to
occur today.

.LONG TERM...(Tuesday night through Monday)
Issued at 219 PM EDT MON MAY 21 2018

Bottom Line:

The primary concerns over the next 3-7 days are dry/warm
conditions leading to elevated fire weather potential on Wednesday
and the potential for showers and thunderstorms Thursday through
Saturday.

Details:

Wednesday: Continued warm and dry conditions are expected Wednesday
as the region remains under the influence of northwesterly flow
aloft. Above average highs in the low to mid 70s along the Great
Lakes to upper 80s in the interior and along the Wisconsin border
are expected. With such warm temperatures, RH percentages will
once again fall in the 20-30% range in the interior west with
relatively light winds of 15 mph or less prevailing. Overall, fire
weather conditions will remain elevated on Wednesday.

Wednesday night/Thursday: By midweek, the area will become under the
influence of a compact slowly-moving shortwave trough embedded in
the northwesterly flow aloft. There is a decent signal in numerical
model guidance that convection will blossom along the nose of a
southeasterly low-level jet/elevated mixed layer late Wednesday
night and early Thursday across portions of Minnesota and Wisconsin.
As the low-level jet weakens Thursday morning, so should the
convection as it nears the Wisconsin/Michigan border. Even so,
surface southwesterly winds will begin transporting moisture back
into the U.P. which, when combined with steepening mid-level
lapse rates associated with the EML moving into the upper Great
Lakes, will lead to an increase in instability by Thursday
afternoon. Now, there is quite a bit of uncertainly with the
potential for renewed convective development on Thursday as
synoptic-scale lift will be absent (e.g. aforementioned trough and
associated forcing will still be far removed to the west) and any
convective debris from morning convection across
Minnesota/Wisconsin would limit diurnal heating. Should the
convection Wednesday night end up being less widespread than
currently advertised, at least isolated redevelopment seems likely
along lake breeze boundaries especially in north central Upper
Michigan where instability would be maximized. A quick look at
forecast kinematic profiles suggests that organized thunderstorms
are unlikely owing to less than optimal 0-6 km bulk shear of 20-25
kts. However low-level curvature in the wind field with a
favorable southeasterly storm motion along any lake breeze would
suggest the potential for perhaps a few dynamically-enhanced
updrafts.

Thursday night to Saturday night: Several rounds of showers and
thunderstorms are possible this weekend but numerical model guidance
varies considerably on the location and amount of any rainfall.
Pattern recognition leads me to believe that the forcing for
convection on Friday and Saturday will be tied to convectively-
generated PV anomalies from upstream thunderstorms in the Upper
Mississippi River Valley. Such features are nearly impossible to
forecast at this range so I won`t pull my hair out trying.
However, it is worth noting that there is *some* potential for a
few strong thunderstorms on Friday and Saturday given forecast
instability in the 1500-2500 J/kg range. Even while weak 0-6 km
bulk shear of 25- 30 kts will tend to limit storm organization,
steep low- and mid-level lapse rates will promote gusty winds and
hail, respectively, in storms that are able to take advantage of
the thermal instability. The strongest thunderstorms will also be
heavy rainfall producers as PWAT values increase to 1-1.25"+
Friday and Saturday. By and large, it looks like some areas may
pick up some decent rainfall this weekend but as is often the case
with convection, others may see close to nothing at all.

Sunday and beyond: Relatively quiet weather is expected to return Sunday
and into early next week as an upper-level ridge builds into the
western Great Lakes.
&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 133 AM EDT TUE MAY 22 2018

With a ridge and a dry air mass lingering, VFR conditions will
prevail at KIWD/KCMX/KSAW through this forecast period with light
winds. However, clouds will thicken over the west overnight near
KIWD with cigs approaching but staying above MVFR.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 431 AM EDT TUE MAY 22 2018

A weak pres gradient will dominate for the next few days, resulting
in winds of 5-15kt across Lake Superior today through Thu. A low
pres system or trough moving across the western Great Lakes on Sat
may lead to somewhat stronger winds at some point Fri/Sat.
&&

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

$$

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



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