Area Forecast Discussion
Issued by NWS Marquette, MI

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917
FXUS63 KMQT 211824
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
224 PM EDT Mon May 21 2018

.SHORT TERM...(Today and tonight)
Issued at 439 AM EDT MON MAY 21 2018

Water vapor imagery and RAP analysis show a deep northern stream
trof over eastern Canada. The flow is split over western N America
with a ridge over western Canada and a trof over the western CONUS.
In the sw flow downstream of the trof, a couple of shortwaves are
over the central Plains. One of the fcst concerns during the short
term will be whether these shortwaves will spread any shra into the
fcst area late today or this evening. Prior to that, fire wx will be
a concern. Currently, skies are clear across the fcst area, though
some high thin clouds are beginning to spread out of WI into Upper
MI ahead of the aforementioned shortwaves. A wide range of temps is
noted with some interior locations down in the low/mid 30s while
temps are as high as the low/mid 50s at some locations near Lake
Superior. Warmest conditions are in the Marquette area.

Some high clouds, mostly thin, will spread across the area today.
Mid clouds should then follow into s central Upper MI during the mid
and late aftn hrs as upstream shortwaves move closer. With high
clouds not providing much restriction to solar insolation, deep
mixing of drier air down from aloft will lead to another day of low
RH. Similar to yesterday, incorporated lower dwpts based on mixing
heights along with bias corrected guidance to arrive at aftn dwpts.
With high temps rising well into the 70s, min RH will likely be in
the 17 to 25pct range for much of the fcst area. Sustained winds
should be up around 9-13mph with gusts in the 15-20mph range,
strongest over the central fcst area. As a result, wildfire
potential will be elevated sufficiently to warrant a special weather
statement to heighten awareness for much of the area today,
particularly the central counties where winds will be strongest.
Under se winds, coolest conditions this aftn will be along Lake MI
and the east side of the Keweenaw.

Shortwave will weaken/shear e across the Great Lakes region tonight
in the more confluent flow across this region. As a result, moisture
transport gets shunted eastward rather than northward into Upper MI.
So, shra potential looks quite limited. As with the late aftn hrs,
will only include shc shra mention across southern Menominee County
this evening. Otherwise, with more cloud cover around tonight,
bumped min temps up a few degrees from previous fcst. 40s will be
the rule.

.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 12Z TAFS through 12Z Tuesday morning)
Issued at 736 AM EDT MON MAY 21 2018

With high pressure and a dry air mass lingering, VFR conditions will
prevail at KIWD/KCMX/KSAW through this forecast period. Light winds
will increase some today, especially at KSAW where gusts to
around 17kt are expected in the aftn.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 439 AM EDT MON MAY 21 2018

A weak pres gradient will dominate for much of this week, leading to
winds less than 20kt across Lake Superior. On most days, winds will
be under 15kt across much of the lake. 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...Rolfson
MARINE...Rolfson



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