Area Forecast Discussion
Issued by NWS Marquette, MI
FXUS63 KMQT 221743
Area Forecast Discussion
National Weather Service Marquette MI
143 PM EDT MON AUG 22 2016
.SHORT TERM...(Today and tonight)
Issued at 505 AM EDT MON AUG 22 2016
Early this morning, surface observations are showing much quieter
conditions than yesterday around this time, with fairly light winds
across the U.P. and temperatures in the low 40s to around 50. Radar
is showing rain showers sliding across the MN/Ontario border this
morning along the Arrowhead of MN. The southward extent is along the
border with the best coverage remaining in Canada. Outside of that
area, satellite data and surface observations are showing mainly
clear skies with a few patches of fog over northern WI and areas of
the U.P. along the WI border. Upstream Raobs continue to show a very
dry sounding through much of the atompshere this morning.
Today: Fairly quiet day expected for most of the U.P. other than
some gusty south to southwest winds. A surface ridge, in place
across the U.P. this morning, will slide eastward throughout the
day. As this happens, the stronger southerly winds will slide in on
the back side of the high. The main impact will be increasing
moisture across the U.P. with the only real chance of rain showers
occurring over north central Lake Superior and there is an outside
chance that the tip of the Keweenaw Peninsula could see and isolated
showers or two. The main feature causing those showers would be the
increasing WAA over that area with added moisture and best
isentropic ascent. Otherwise, the aforementioned area will likely
see increased cloud cover, while the rest of the U.P. sees partly
cloudy skies. High temperatures will be warmer than normal as 850mb
temperatures increase to around 12C to 15C by late afternoon. 80
degree temperatures are not out of the question over the western
portion of the U.P. and especially in the southwest wind downslope
locations. These areas will be closes to the 850mb ridge axis.
Tonight: As the high pressure center continues eastward, WAA and
moisture advection will continue into the Upper Great Lakes Region.
At the same time, a fairly strong 40 to 50 knot LLJ is expected to
develop from the Plains into northern WI. The added moisture
transport along with the U.P. being right on the nose of the LLJ it
is not out of the question that rain showers and maybe an isolated
thunderstorm could develop after about 02Z/23. This will be where
the best low level convergence would be; however, the main limiting
factor will be just how quickly moisture is able to slide into the
CWA. Soundings continue to show very dry air through most layers of
the sounding, which would lean against any sort of widespread
showers. At this point, have decided to stick with isolated showers
due to the main limiting factor as just mentioned. Even if showers
don`t develop across the area it is likely that there will be at
least an increase in cloud cover. Winds could be fairly gusty in the
evening hours as LLJ begins to develop; however, it does look like
there may be some decoupling that occurs later in the night, which
may help to decrease the surface winds a bit. Temperatures will be
warmer than normal with continued WAA along with the potential for
increased cloud cover. Most areas will be in the 60s for overnight
lows with perhaps the warmest locations being in the favored
southwest-wind downslope areas along Lake Superior.
.LONG TERM...(Tuesday through Sunday)
Issued at 458 AM EDT MON AUG 22 2016
Models suggest that a progressive pattern will prevail with a
mid/upper level low/trough over srn Alberta/Sask Tuesday will move to
nrn Ontario by Thursday. This will bring unseasonably warm air into
the wrn Great Lakes with waa ahead of the sfc low Tuesday and
increasing shra/tsra chances Wednesday as the sfc trough/front moves
into the region. Cooler and drier weather will then move in from
Thursday into Friday as high pressure builds from the nrn plains into
the Great Lakes. Unsettled weather returns by the weekend as the low
amplitude pattern will allow another mid level trough to move into
Tuesday, continued waa and increasing mid level capping will will
preclude any pcpn chances and allow temps to climb well above
normal. Forecast mixing heights into the 900-850 mb range support
highs into the mid to upper 80s with dewpoints into the lower 60s.
Wednesday and Wednesday night, as the sfc trough moves into the area
expect shra/tsra chances to increase by late wed into wed night as
moisture advection bring PWAT values above 1.5 inches. However, only
chance pops were included with uncertainty remaining with the
timing/position/strength of any convectively modified shortwaves
emerging from the plains that will help support the pcpn.
Instability (MLCAPE values into the 500-1000 J/Kg range) and shear(0-
6km to 30 knots) will be marginal for any stronger storms. The pcpn
chances will shift to mainly the ern cwa by Thursday morning.
Thursday, a trailing secondary cold front and shrtwv could bring
some isold -shra into the nw cwa. Otherwise, cooler air and drier
air will prevail with highs from the upper 60s west to mid 70s
south and east and dewpoints falling into the mid 50s.
Friday-Sunday, surface high pressure and upper ridging will then
bring dry and mostly clear conditions Friday into early Saturday.
With a continued progressive pattern, pcpn chances will increase as
models suggest potential for a shrtwv to bring another round of
shra/tsra toward the area from later Saturday into Sunday. However,
confidence in any details is low given models differences and lack
.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 142 PM EDT MON AUG 22 2016
VFR conditions are expected for all sites through the period. Main
concern will be LLWS developing at KIWD and KSAW as a strong low-
level jet forms this evening and persists through daybreak Tuesday.
There are some indications that SW winds up to 50kts will be possible
as low as 1kft AGL. Otherwise, some -SHRA and possibly thunder will
be possible for KSAW tonight.
.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 505 AM EDT MON AUG 22 2016
A high pressure ridge will continue to slide east of the U.P.
today causing winds to become or remain south to southwesterly
through the day. The pressure gradient is expected to tighten today
through Tuesday between this departing high pressure center and an
approaching cold front, so expect the SSW winds to pick up to 20-25
kts again as early as tonight and then continue at times through
Wednesday. Winds will then shift to the west and west-northwest up
to 25 kts following the cold frontal passage Wednesday evening.
These gusty winds will linger through Thursday morning before slowly
diminishing below 20 knots in the afternoon. After the trailing high
pressure center shifts to the east on Friday, winds will shift back
to the southwest at less than 15 knots.