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Area forecast discussion 
National Weather Service Hastings NE
659 am CDT Thursday Oct 23 2014

issued at 634 am CDT Thursday Oct 23 2014 much for possibly being able to keep a handful of our
eastern/southeastern-most counties out of the dense fog advisory.
Mainly over the past 60-90 minutes...several areas down Highway
81 from York-Hebron and down into Jewell/Mitchell counties in Kansas
have started to tank down to around 1/4 mile or less per automated
observation and several phone calls. This really shouldn/T be a surprise
as even though this particular area was not well-captured by the
hrrr/rap13 visibility forecasts...the ambient conditions are very
similar to the remainder of the County Warning Area and as the boundary layer
cooled fog readily formed there as well. On a side note...although
dense fog is obviously not all that uncommon around here...its
not everyday that literally all 13 primary automated Airport
ASOS/AWOS sites within our County Warning Area (along with several sites just
outside our cwa) report visibility of one-quarter mile or less at
the same time.


Short term...(today and tonight)
issued at 445 am CDT Thursday Oct 23 2014

Although confidence is rather high in a dry 24 hours...the main
forecast issue has now turned to widespread fog for this
morning (much of which is dense)...and there are plenty of
questions regarding just how long this fog and/or low stratus will
last and how much effect it might have on afternoon high temperatures.
Although its not out of the question that a more limited/patchy
round of fog could again materialize for Thursday night...have
opted against forecast inclusion at this time given that the low-
level environment should be considerably more mixed and
inhospitable to widespread issues.

Starting with the current scene as of 09z/4am...although the
possibility of impactful fog was recognized here 24 hours
ago...kudos to previous day shift for hitting the throttle harder
with a large percentage of the County Warning Area is currently
experiencing visibilities around/less than 1/4 mile per automated
Airport observation and Highway cams...and a dense fog advisory is out for
the majority of the County Warning Area through 16z/11am. At least so
far...mainly only the far eastern counties from York-Hebron-
Beloit seem to be missing out on widespread dense fog
issues...likely in part to holding up a bit warmer in the wake of
the departing cloud shield from yesterday/S low pressure system.
Although this could easily change over the next few
hours...short-term modeled visibility from the latest rap13/hrrr
suggest we may get away without needing to expand the advisory
again...time will tell. Obviously two of the biggest factors in
fog formation were freshly wet ground from widespread rain
yesterday (which neared or exceeded 1 inch in a bit more of the
area than expected) and very light to near-calm breezes along the
axis of a weak cold front that has essentially washed out across
the County Warning Area in a southwest-to-northeast fashion. Low temperatures this
morning appear to be working out fairly well...with a decent range
from low-middle 40s northwest to low-middle 50s southeast. In the big
picture of the middle-upper levels...water vapor imagery and short
term model data confirms that the County Warning Area is now just behind the
departing shortwave trough axis that brought yesterday/S
rain...with this axis generally aligned along the MO River Valley.

Looking ahead forecast-wise...needless to say the number one issue
and question is how long does dense fog linger...and could low
stratus stick around long enough to hamper high temperatures especially
in the eastern County Warning Area.

Based on the usually fairly-reliable short term modeled visibility
from the hrrr/ may be well into the middle-late morning
hours before an appreciable percentage of the County Warning Area shakes free of
widespread fog issues. As a result...opted to extend the advisory
time an hour or two longer than "usual" to 16z/ would
rather have day shift be able to cancel some counties early than
have to issue extensions. Although much of this fog is likely
fairly shallow...the low-level environment will likely not support
a rapid fog dissipation given appreciable boundary layer
saturation and only very weak mixing as a broad surface ridge axis
migrates through the area and keeps breezes very light. Eventually
as the afternoon wears on...a steadier 5-10 miles per hour southerly breeze
will kick response to subtle pressure falls to the west
and northwest. Although these sort of situations make for very
tricky sky cover/temperature forecasts...the general expectation
is for plenty of fog/low clouds this morning to gradually give way
to no-worse-than partly cloudy skies this afternoon...although
the earliest clearing might very well target the western County Warning Area first
and portions of the central/east last. Adding to the temperature
uncertainty is a notable 10-ish degree spread between NAM met
(cooler) and GFS mav (warmer) numerical guidance today. If
anything...have probably aimed forecast highs a touch on the
pessimistic side by lowering 2-3 degrees from previous forecast
across much of the County Warning Area...but for now will run with upper 60s to
near 70 across much of the central/east and more in the way of
middle-70s far west. There could be at least some modest coverage of
high cirrus this afternoon as some high clouds spill east-
southeast into the area in association with a fairly low amplitude
disturbance tracking mainly from the northern rockies into the

For this evening/tonight...aforementioned fairly weak
disturbances just to the northwest of the local area will slide
east-southeast over the Central Plains...riding around the edge of
a broad middle-upper ridge edging north-northeast out of the Desert
Southwest. As a weak low pressure axis extending southward into
the Central Plains out of the Dakotas/Canada brushes through the
region tonight...the low level environment should be considerably
more inhospitable to impactful fog formation as south-
southwesterly breezes become fairly steady at 5-10 miles per hour and locally
higher. That being few shifts will want to keep an eye
on at least limited/patchy fog potential as somewhat strangely the
06z NAM visibility product is hitting parts of the County Warning Area harder than
seems justified late tonight. Thanks mainly to the steadier
southerly breezes and at least some degree of passing high cloud
cover...a seasonably mild night is in store and nudged low temperatures
generally 1-2 degrees upward from previous forecast in most
areas...keeping most of the County Warning Area up in the low-middle 50s except a
greater likelihood of some 40s in far western/northern counties.

Long term...(friday through wednesday)
issued at 445 am CDT Thursday Oct 23 2014

Above normal temperatures and dry weather will be the rule through
the majority of the period.

The forecast pattern suggests a long wave trough will move inland
off the West Coast late in the weekend. The trough is forecast to
progress across the area and exit to the east by Tuesday. Otherwise
benign weather is expected to continue as a zonal pattern persists.

So...specifically...we expect much above normal temperatures Friday
through Monday...then a cool front is expected to move through by
Monday afternoon. A few showers are hard to completely rule out in
the vicinity of the front. Currently it appears any rain that occurs
Monday through Monday evening would be very light and most likely
sprinkles at best. Near normal temperatures are expected Tuesday and
Wednesday with dry conditions continuing.

Friday afternoon presents a concern in terms of fire weather. The
area is forecast to see relative humidities drop below 25% through
the afternoon hours...but currently winds are expected to be 15 miles per hour
or less. So...current forecast conditions do not warrant a mention
of any fire danger at this point...but we will continue to


Aviation...(for the 12z kgri/kear tafs through 12z Friday morning)
issued at 659 am CDT Thursday Oct 23 2014

By far the primary aviation issue is the ongoing/rather widespread
coverage of dense fog within south central Nebraska resulting in
LIFR/vlifr visibility and ceiling. Although confidence is a bit
shaky on the timing of improvement in conditions...opted to stay
the course with previous taf issuances in returning visibility to
VFR around 16z and also raising ceiling to MVFR at this time. Then
in the 19z-20z time frame this afternoon have advertised a return
to VFR ceiling as well. Stay tuned for plenty of potential
adjustments here. Although some haze/mainly light fog probably
cannot be ruled out completely again tonight...the environment
should not be as favorable for dense fog development and have only
hinted at low probability of fog with a low-end VFR visibility and
low scattered cloud mention for now. Also late tonight...later
shifts may have to consider whether a low level wind shear (llws)
mention may be increasing westerly winds in the
lowest 1000 feet above ground level could create around 30kt of bulk shear
difference between the surface and this level. This seemed too
marginal a wind shear event for inclusion at this time. At least
confidence is high in dry conditions through the period...and
surface winds should not be much of an issue with a light/variable
regime this morning eventually becoming more established from the
south-southwest this afternoon into tonight...but at sustained
speeds generally only around 10kt.


Gid watches/warnings/advisories...
NE...dense fog advisory until 11 am CDT this morning for nez039>041-

Kansas...dense fog advisory until 11 am CDT this morning for ksz005>007-



short term...pfannkuch
long term...eddy

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