Forecast discussions (also known as a FPUS, FPUS3, AFD, or SFD)
are issued by every National Weather Service
office, and you can use them to get a glimpse into the mind of the
duty forecaster. Forecast discussions can be obtained from
databases like
IWIN
and other sources.
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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPRINGFIELD MO
200 PM CST MON JAN 14 2001
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This is the standard heading. Pretty standard fare.
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DILEMMA DU JOUR: DO WE NEED A HEADLINE FOR TUESDAY NIGHT?
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A headline is a term for a "banner" that is often placed at the top
of the National Weather Service forecast during major weather
events to emphasize the importance to
media weathercasters and other users.
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RIDGE OF HIGH PRESSURE ACROSS THE CENTRAL AND SOUTHERN PLAINS HAD
PRODUCED A SUNNY BUT COOL DAY ACROSS THE FORECAST AREA. STUBBORN
AREA OF LOW CLOUDS CONTINUED TO SKIRT THE FAR NORTHEASTERN EDGE OF
THE FORECAST AREA...WITH HIGH CLOUDS STREAMING INTO SOUTHWESTERN
SECTIONS ON A 130 KNOT JET.
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A ridge of high pressure (which can be either at the surface or aloft)
is often associated with good weather. Typically there is subsidence
(sinking) within the ridge. The forecaster mentions stubborn low
clouds, indicating that they might have played havoc with the
forecast for that area, and that high clouds are riding in
swiftly on a strong 130 knot (150 mph) jet stream.
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MODELS STILL HAVE THEIR DIFFERENCES WITH THE NEXT SYSTEM TO AFFECT
THE OZARKS: AVN REMAINS THE STRONGEST AND FARTHEST NORTHWEST WHILE
THE ETA/MESOETA ARE MORE PROGRESSIVE AND WEAKER. LEANING TOWARD THE
ETA/MESOETA SOLUTION TODAY...AS THE AVN MAY BE TRYING TO ABSORB THE
WAVE INTO THE NORTHERN STREAM SYSTEM TOO FAST.
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The forecaster has looked at the computer-generated model forecasts
and figures that there are differences between the different types
of models. The AVN (also known as GSM and MRF) show stronger
systems (larger upper-level waves and deeper surface systems) with
most of the region's weather features biased toward the northwest,
while the ETA solutions are more progressive (shallow waves and
shallow surface systems, which tend to move rapidly with the
upper-level flow). The forecaster prefers the ETA solution,
however the reason did not make sense (at least to me).
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CLOUDS WILL CONTINUE TO INCREASE THIS AFTERNOON/TONIGHT AS SHORT
WAVE CIRCULATES AROUND THE DEVELOPING LOW IN THE DESERT SOUTHWEST
AND MOVES INTO THE SOUTHERN PLAINS TUESDAY MORNING.
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The proximity of the upper-level low to the southwest will generate
clouds for the area because it will create dynamic lift and will
be the focus for embedded upper-level disturbances that rotate
around it
(see the 500 mb chart). These will
increase as the upper-level low approaches.
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TWO WAVES OF LIFT EXPECTED ACROSS THE REGION: FIRST WILL COME AS A
COUPLED JET SIGNATURE MOVES ACROSS THE OZARKS TUESDAY AFTERNOON.
SECOND WILL BE TUESDAY NIGHT WHEN ACTUAL SHORT WAVE MOVES THROUGH.
ODD THING ABOUT THIS EVENT IS THAT ALL OF THE LIFT IS ABOVE 700 MB.
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It appears here that the forecaster expects a right-rear quadrant
of a polar jet will couple with the left-front quadrant of a subtropical jet,
which can produce enhanced upward motion. This will be followed by
lift from an upper-level disturbance. The forecaster notices from
the model output that all of the lift occurs above 10,000 ft (700 mb),
which is indicative of considerable dry air in the lower troposphere
or possible shortfalls in the model solutions.
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CURRENT FORECAST HAS ONE TO TWO INCHES OF SNOW ACCUMULATION AND SEE
NO NEED TO DEVIATE FROM THIS IDEA. DO NOT BELIEVE THAT ANY HEADLINE
IS NEEDED AT THIS POINT...BUT LATER SHIFTS WILL HAVE TO REEVALUATE.
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Pretty obvious wording. There is some concern that headlines will
need to be added to the forecasts, but this will be left to later
forecasting shifts.
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EXTENDED FORECAST LOOKS COOL BUT DRY FOR THE MOST PART. THINGS GET
UGLY FRIDAY AS NORTHERN AND SOUTHERN STREAM SYSTEMS MEET OVER THE
MIDDLE MISSISSIPPI VALLEY BEFORE CREATING A STRONG STORM FOR THE
EAST COAST. NOT MUCH IN THE WAY OF PRECIPITATION EXPECTED...WITH
NORTHERN STREAM SYSTEMS STARVED FOR MOISTURE AND GULF RETURN LIMITED
BY PRECIPITATION ALONG THE COAST. WILL ADD A CHANCE OF LIGHT SNOW
FOR FRIDAY WITH HIGHEST CHANCES IN SOUTHEAST SECTIONS.
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A jet stream segment across the southern US and the northern US
as well as two upper-level disturbances will come in close proximity
with each other
(see 500 mb chart).
This indicates that the atmosphere is highly baroclinic (contains
strong air mass contrasts) and is a breeding ground for strong
weather systems to develop. Obviously the threat area will be
downstream from these two regions: the east coast. The sentence
about "not much in the way of precipitation" applies only to
the Kansas City region, and was written since the southern
system will be ingesting much of the moisture that could have
been destined for the Kansas City area, and the northern system
due to the pattern and its northerly position will be dry.
However the forecaster feels there is enough of a threat from
the proximity of the systems to add in a chance for snow.
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THANKS TO TED AT STL FOR COORDINATION THIS AFTERNOON
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The forecasters occasionally coordinate their predictions with
other offices; in this case it was the St. Louis office.
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PRELIMINARY GUIDANCE FOR COORDINATION PURPOSES ONLY
SGF 023 035 023 030 020 / 5 40 70 20
JLN 024 036 023 031 022 / 5 70 70 10
UNO 025 038 025 032 023 / 0 30 70 30
VIH 022 034 022 029 018 / 0 30 70 30
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This is coded temperature and precipitation forecasts. The first
line reads Springfield, low tonight 23, high tomorrow 35, low
next night 23, high next day 30, low next night 20. Chance of
precipitation 5% tonight, 40% tomorrow, 70% the next night, and
20% the following day.
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.SGF...
KS...NONE
MO...NONE
SUTTON
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No warnings or watches are in effect for the region. The
forecaster's last name is Sutton.
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FXUS64 KOUN 112159 COR
AFDOKC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORMAN OK
351 PM CST MON DEC 11 2000
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This is the bulletin header. It was prepared by a forecaster
at the NWS in Norman, Oklahoma, and was issued at 3:51 pm
on December 11, 2000.
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COLDEST AIR IN ALMOST FOUR YEARS HAS TIGHTENED ITS GRIP ON THE
SOUTHERN PLAINS...WITH DAYTIME TEMPERATURES HOLDING IN THE TEENS
ACROSS CENTRAL AND NORTHERN OKLAHOMA. AS CAA ABATES...AND CENTER OF
SURFACE HIGH APPROACHES...STRATUS SHOULD ERODE...ALLOWING FOR A
STRONG RADITIONAL COOLING NIGHT...WITH TEMPS EXPECTED TO DIP INTO
THE SINGLE DIGITS ACROSS MOST OF THE CWA. WOULDN'T BE SURPRISED TO
SEE A FEW LOCATIONS IN NOTHERN OKLAHOMA DIP BELOW ZERO.
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Cold high pressure is moving in, and the downward motion within the
high pressure area will allow the low stratus clouds to erode.
This will create clear skies, which allows the ground to radiate
heat into outer space. This will result in strong cooling across
the county warning area (CWA).
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CLOUDS WILL ONCE AGAIN INCREASE TOMORROW ACROSS THE AREA AHEAD OF
FAST MOVING SHORTWAVE CURRENTLY OFF THE CALIFORNIA COAST.
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A short wave is a somewhat ambiguous term for a disturbance in the
upper-level flow that produces upward motion (i.e. it tends to produce
clouds and rain). There is one that will be approaching from the
southern California coast, and it will likely produce clouds and
upward motion.
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FORECAST THEN GETS EXTREMELY TRICKY...WITH POSSIBILITY OF WINTER PRECIP EVENT
LOOMING TOMORROW AFTERNOON/EVENING. STUCK CLOSELY WITH ETA SOLUTION
FOR THIS PACKAGE...AS AVN APPEARS TO PLACE QPF TOO FAR TO THE
NORTH...GIVEN FORECAST WAA FIELDS...AND TRACK OF SHORTWAVE.
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The ETA model (equivalent to the Greek letter "eta") is one of the best
forecasting models in use today. Here it forecasted winter precipitation.
The AVN, also known as the GSM and MRF, is an older but updated model
that is more accurate in large-scale rather than small-scale depictions.
It placed the quantitative precipitation forecast (QPF) of precipitation
too far north. The forecaster assumed that the best warm air advection
would be further to the south (over Texas), which implies the ETA run
is doing a better job.
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AVN HAS BEEN CONSISTENT FROM RUN-TO-RUN IN DEVELOPING SLIGHTLY STRONGER
SHORTWAVE THAN ETA. TRACKS BETWEEN THE TWO MODELS ARE VERY
SIMILAR...SO FEEL SOMEWHAT CONFIDENT IN WHERE THE HEAVIEST PRECIP
WILL OCCUR...BUT AM LESS CONFIDENT CONCERNING HOW HEAVY IT WILL BE.
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Back to the AVN/GSM/MRF, which is great with large-scale patterns. It
developed a stronger upper-air disturbance, which intrigues the forecaster.
The AVN and ETA show a similar forecast track for the disturbance,
but there is some question how strong it will be.
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WAA BEGINS TO INCREASE IN MID LEVELS TOMORROW AFTERNOON...MAINLY
ACROSS NORTH TEXAS/SOUTHERN OKLAHOMA IN ADVANCE OF LEAD SHORTWAVE.
THEREFORE...WILL MAINTAIN POPS TO ACCOUNT FOR THIS.
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Warm air advection (WAA) throughout the middle level of the atmosphere
(about 10,000 to 20,000 ft, or 700 to 500 mb), is expected to increase.
This supports upward vertical motion. Therefore the forecaster will maintain
significant probability of precipitation numbers (POPs) in his forecast to account
for this.
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WITH MAIN WAVE KICKING OUT TOMORROW NIGHT...WILL INCREASE POPS FURTHER...AGAIN
MAINLY ACROSS SOUTHERN ZONES. ETA FORECAST SOUNDINGS INDICATE THAT
ANY PRECIP WILL LIKELY BE IN THE FORM OF SNOW.
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Warm air advection in combination with lift from a short wave disturbance
is a fairly substantial indicator of upward motion. Therefore as the
warm air advection phases with the short wave, the forecaster is
further boosting the odds of precipitation. The forecast soundings
(vertical temperature profiles) indicate snow, which likely means that
the entire column of air is subfreezing and will produce ice particles.
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WITH INTENSITY OF FORCING...ANTICIPATE THE POSSIBILITY OF SOME
SIGNIFICANT SNOWFALL TOTALS...SO WILL ISSUE WINTER STORM WATCH...
MAINLY FOR NORTH TEXAS
AND PORTIONS OF SOUTHERN OKLAHOMA.
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Although the model forecasts aren't clear on the strength of the short wave,
the forecaster feels there will be enough warm advection and/or lift from
the short wave to produce strong lift and thus significant precipitation.
With this and the fact that the forecast sounding shows subfreezing
temperatures, snow is the best bet.
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WITH SPEED OF SHORTWAVE...WINTRY PRECIP SHOULD NOT LINGER TOO LONG
INTO WEDNESDAY...AND WILL BEGIN TO CLEAR THINGS OUT WED AND WED
NIGHT. THURSDAY AND FRIDAY WILL SEE SOME RECOVERY FROM THE ARCTIC
AIRMASS...WITH HIGH TEMPS EXPECTED TO WARM INTO THE 40S BY FRIDAY.
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The disturbance will rapidly take the bad weather with it, and for
reasons not specified (probably high pressure and a ridge aloft),
clear skies are forecast with warming.
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MAJOR CHANGES INTRODUCED FOR THE WEEKEND FROM PREVIOUS PACKAGES...AS
MRF...CANADIAN...AND EUROPEAN ALL FAIRLY CONSISTENT IN BRINGING
ANOTHER SHOT OF ARCTIC AIR INTO THE AREA. WILL ALSO INCLUDE SLIGHT
POPS FOR SATURDAY FOR ANY LIGHT SNOW/FREEZING DRIZZLE DEVELOPING
BEHIND ARCTIC FRONT.
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The forecaster has seen the latest AVN/GSM/MRF run, along with Canadian
and European (ECMWF) models, and this shows more arctic air coming into
the area. The forecaster feels that more precipitation is a possibility
with it, probably because of mid-level warm air advection and/or
a short wave disturbance.
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JL
FCSTID = 4
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The forecaster's initials are JL, and his office ID is 4.
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OKC 4 22 17 25 / 0 30 50 30
HBR 8 21 16 26 / 0 50 50 30
SPS 11 26 20 28 / 0 60 70 40
GAG 1 19 15 24 / 0 30 30 30
PNC 0 18 16 24 / 0 0 30 30
DUA 11 25 20 28 / 0 60 60 40
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These are quantitative forecast numbers. The first group is the
min and max temperatures, and the second group is the probability
of precipitation in percent. Translated, for Oklahoma City (OKC),
the next day's forecast low is 4 deg F, with the high 22, and the
following day the low will be 17 with a high of 25. The next
day's chance of precipitation is 0% in the morning and 30% in
the evening. The following day, the chances are 50% in the
morning and 30% in the evening.
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.OUN...
OK...WINTER STORM WATCH TUE AFTN AND TUE NIGHT ZONES
OKZ036>039-041-043-045>048-050>052.
TX...WINTER STORM WATCH TUE AFTN AND TUE NIGHT ZONES TXZ083>090.
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This group indicates what watches and advisories are in effect,
along with the zone numbers that they are assigned to.
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