Area forecast discussion
National Weather Service Duluth Minnesota
501 PM CDT Sat may 18 2013
Update...
updated to add dense fog advisory in twin ports area and North
Shore where visibilities have been at or below 1/2 mile. Coq and gna have
reported zero at times. Expect this continue through the night.
&&
Previous discussion... /issued 424 PM CDT Sat may 18 2013/
Short term...tonight and Sunday...
low level warm frontal zone has become well established along and
just south of the i94 corridor late this afternoon. Areas along
and north of this frontal zone will be the focus area for
additional showers and thunderstorms overnight and Sunday morning.
By late this evening and 30-40 knots southerly low level jet will
develop and interact with the frontal zone. This will enhance
warm/moist advection in the lowest levels..and also result in
increased frontogenetic forcing for mesoscale ascent. The result
is expected to be redevelopment of rather widespread
showers/thunderstorms overnight. Influx of 1.5 to 1.7 inch precipitation water
amounts /almost 300% of climatology normals for middle may/ further
supports heavy rainfall potential overnight/Sunday morning.
Thus..we have hoisted a Flash Flood Watch for Cass/Crow
Wing/Aitkin counties where 1-3 inches of rain already fell this
morning. There is still some uncertainty as to the exact location
where storms will redevelop..so the watch may need to be
adjusted/expanded according to convective trends later this
evening.
Large scale trough and surface low will continue to slowly deepen
while moving toward Minnesota on Sunday..with little northward
progress of the warm front. Thus..there should be a continued flux
of warm/moist/unstable air into the region supporting additional
showers/tstorms. Also..as surface low deepens to our southwest and
high pressure builds northeast of Lake Superior..easterly gradient
should allow for fairly gusty east-northeast winds in vicinity of Lake Superior later
Sunday. In general..we went below guidance on temperatures..as
combination of clouds/precipitation and easterly flow favor smaller
diurnal temperature range for Sunday. The one exception is the far southeast
portion of the County Warning Area..which could get into the surface warm sector
Sunday afternoon with temperatures/dewpoints reaching the lower 80s
/Lower-Middle 60s.
Long term...Sunday night through Saturday...
focus during this period will continue to be on the very slow
moving low pressure system. The models are in decent
agreement...with a general consensus of the surface and upper low
over the South Dakota/Nebraska area at 00z Monday. They only then
move it slowly east by 00z Wednesday...placing the low anywhere from
southwest Minnesota...to the Nebraska/Iowa border depending on the
model. What these means for most of the Northland is plenty of
rain and thunderstorms Sunday night through Wednesday...although
chances will diminish across the north Tuesday into Wednesday.
Plenty of moisture will remain over the region with precipitable water values
from 1.25 to around 1.50 inches. This will provide plenty fuel for
rain.
Significant rainfall is looking likely Sunday night into
Wednesday...and this is on top of rain that fell last night/today
and is expected tonight/Sunday. Another 1 to 3 inches of
rain...possibly more given the possibility of thunderstorms and
training storms...is expected Sunday night into Tuesday evening.
We've already seen a sharp rise in the rivers over far northern
Wisconsin. The threat for some flooding is increasing...but the
extent is difficult to determine at this point. There is a Flash
Flood Watch for portions of the Northland tonight...and additional
watches may be needed Sunday night into early next week depending on
how things develop tonight into Sunday.
Precipitation chances should diminish significantly Wednesday night...with
most areas dry Thursday.
Ridging will provide dry conditions over much of the region Thursday
into Friday night. We bring in a chance for showers into our far
west next Saturday...but the 12z European model (ecmwf) is slower and would suggest
another dry day.
Aviation...18z taf issuance...
much of the Northland was under IFR or low MVFR ceilings with
light rain/drizzle. Dense fog was occurring around Lake Superior
as well with a moist onshore flow. We expect the current rain to
continue to move east and north this afternoon...with
redevelopment likely later this afternoon into tonight. Moist flow
over a warm front which remains to the south of the Northland will
become a focus for more showers/storms today. Various models
support development over the Dakotas/Minnesota border region...then they
move the showers/storms east/northeast.
We did increase visibilities at kdlh around 21z...but confidence in this
is lower than average. We followed the rap...as it showed middle-
upper level clouds diminishing and that should allow the sun to
work on the stratus and may be enough to boost visibilities. We think fog
will come back in again this evening lower visibilities again.
&&
Point temps/pops...
dlh 50 61 50 53 / 90 80 80 80
inl 52 62 52 58 / 80 80 70 70
brd 61 71 57 66 / 90 80 80 80
hyr 61 76 61 74 / 60 80 70 80
asx 53 65 52 59 / 60 70 80 80
&&
Dlh watches/warnings/advisories...
Minnesota...Flash Flood Watch from 9 PM CDT this evening through Sunday
afternoon for mnz025-033>036.
Dense fog advisory until 10 am CDT Sunday for mnz020-021-037.
WI...dense fog advisory until 10 am CDT Sunday for wiz001.
Ls...none.
&&
$$
Short term...clc/Miller
long term....melde
