A polar low which developed off of California and was mentioned in a post yesterday, has made landfall in southern Oregon after brushing the northern California coastline. There were many reports of winds in excess of tropical storm force in association with the system in California and Oregon. A short term forecast released a few hours prior to landfall by the NWS office in Eureka, CA, outlined the expected impacts from the low:

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SHORT TERM FORECAST
NATIONAL WEATHER SERVICE EUREKA CA
703 AM PST SUN FEB 24 2008

.NOW..
THROUGH 900 AM…A STRONG…BUT A SLOWLY WEAKENING LOW PRESSURE
SYSTEM LOCATED 60 MILES OFFSHORE OF CAPE MENDOCINO…WILL TRACK
NORTHWEST AT 25 MPH. THIS MOTION WILL BRING THE CENTER OF THE LOW
ONSHORE NEAR CRESCENT CITY BY NOON. ROTATING BANDS OF MODERATE TO
OCCASIONALLY HEAVY SHOWERS AND GUSTY SOUTHEAST WINDS OF 20 TO 30
MPH WILL SPREAD ACROSS THE REDWOOD COAST THIS MORNING.

LIGHTER SHOWERS…BUT VERY WINDY CONDITIONS WILL PERSIST ALONG THE
MENDOCINO COUNTY COAST THROUGH LATE MORNING. SOUTH AND SOUTHEAST
WINDS OF 25 TO 40 MPH SHOULD BE EXPECTED…WITH ADDITIONAL POWER
OUTAGES AND DOWNED TREES LIKELY THROUGH NOON TIME.

LARGE AND DANGEROUS SURF WILL CONTINUE ALONG NORTHWEST CALIFORNIA
COAST ALL DAY. WALKS ON BEACHES OR JETTIES IS HIGHLY DISCOURAGED.

OVER INLAND AREAS…A SNOW ADVISORY REMAINS POSTED THROUGH MID
AFTERNOON FOR ELEVATIONS ABOVE 3500 FEET. IN THE COLDER VALLEYS
OF TRINITY COUNTY SNOW LEVELS WILL HOLD AROUND 2000 FEET THIS
MORNING BEFORE RISING BY MIDDAY. MORNING COMMUTERS ALONG HIGHWAY
299 EAST OF BURNT RANCH SHOULD BE PREPARED FOR SLICK ROADWAYS.

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One would think this was a tropical storm based on its impacts if it wasn’t for the snow that occurred with this at higher elevations!

Below are two satellite shots and one radar shot of the polar low prior to landfall, when it still had an impressive structure. An eye like feature is apparent in all imagery, and the low bears a striking resemblance to a tropical cyclone.

Click to enlarge radar image.

Relating back to my first post on this, both the NAM and the GFS have reached a consensus of painting lower 60’s dewpoints in the warm sector on Monday, in essence the middle point between extremities presented in my original post.

It seems that the main issue for this one will be lack of directional shear, and the continued possibility of moisture mixing out. Models have trended slightly weaker with the 500mb disturbance. SPC seems to have the right idea with a SEE TEXT on the Day 2 outlook, and I do not see anything higher than a low end SLGT risk to verify on Monday over the Southeast.

The next possible event looks to be around 9-10 days away, but there is plenty of time to watch that. As of right now it’s still in “possible threat” mode. More updates to come on this over the coming days as the models get a better hold over the system.

EF2 tornadoes are widely considered “significant tornadoes” in the meteorological community. But I’ve recently left myself to ponder whether or not EF2s are “significant.”

In order to answer this question, I must ask myself what is really meant by “significant.” Is significant determined by historical precident or by effect on human life? Statistically, EF2 tornadoes are fairly common, with well over one hundred occurring each year. So statistically, in the historical record, EF2 tornadoes are not overly significant. The question then boils down to effects on human life. A low-end EF2 can be rated as such by simply destroying a barn, whereas a high-end EF2 can do tens of millions of dollars in damage to a city. A low-end EF2 will generally not destroy a frame house, whereas a high-end EF2 generally will.

So the answer to this question lies in rather gray area. In my opinion, not all EF2s are significant. Some, such as the Springfield, IL, tornadoes of March 12th, 2006, which produced one hundred million dollars of damage and rendered 1000 homes uninhabitable, are. Others, such as the Macon County, IL, tornado of April 2nd, 2006, which destroyed a large barn, are not. Well-constructed arguments can be made in both directions. My opinion is that, in general, a low-end EF2 is not significant, a high-end EF2 is, and the line is drawn about in the middle.

And that’s Tony’s Tantrum of the week for this week.

A baroclinic system active off of the United States west coast has occluded to the point that it has developed a warm air seclusion near its center. Essentially, this means that there is a pocket of warm air at the center of this system surrounded by colder environmental air. This has provided a conducive environment for the development of a polar low, and one has developed. A polar low is comparable to a tropical cyclone, in that it is partially powered off of latent heat of condensation from low-level convection that develops in the warm pocket. However, cold air remains present aloft in situations like this so the cyclone can’t be considered tropical but, it can be considered sub-tropical.

A polar low formed 2 years ago around this time and hit Oregon, bringing wind and rain. This low appears to have its sights on California, so I will be updating on it for the next few days. Below is a visible loop of the polar low (which is at the center of the overall cyclone), an image of low topped convection that is developing around the polar low, and a phase diagram showing the thermodynamic nature of the polar low. The polar low is currently showing up as a shallow warm core on the phase diagram, which as explained before means that it has warm air at the core near the surface with a cold core aloft.

A major severe weather event was expected. There had been severe weather during the day. But no one quite expected what was to come. The night of February 22nd-23rd, 1998, would be the incredible herald to what would be the deadliest tornado season in twenty-four years. At its end, forty-two people would lose their lives across central Florida as seven tornadoes, three of them at F3 intensity, would rip through under cover of darkness.

We here at tornadotony.com dedicate this blog post to the forty-two people that passed away that night, as well as the eighty-eight additional people that would be killed during the horrific 1998 tornado season. Below are links to the NWS service assessment, the NWS damage survey, and the Melbourne, FL, NWS page on the outbreak.

Service Assessment

Damage Survey

NWS Melbourne, FL, page

A rare tornado outbreak occurred in South Florida on 2/12/2008, prompting 13 tornado warnings with 2 confirmed tornadoes. There were undoubtedly more tornadoes but, due to the rural nature of the Everglades there was no one there to confirm many of them. Some structural and tree damage was reported with each tornado. Below are links to the detailed summary on this event just released by the NWS.

Main Page:

http://www.srh.noaa.gov/mfl/events/?id=2008feb12

Warning Summary:

http://www.srh.noaa.gov/mfl/events/?id=2008feb12_pg2

….could not be more different, regarding dewpoints.

The reason may be because the NAM develops some sort of mesolow over the Yucatan Peninsula, which induces some weak northerly surface flow over the Bay of Campeche. The GFS may also be overdoing the dewpoints just a tad; veered low level flow may mix some dry air down to the surface (although, again, the NAM is overdoing it just a bit, IMHO, not to mention it is complete trash 84 hr out).

This post ties into the the severe threat next Monday in the Lower Mississippi Valley, which will be discussed in the coming days.

SEL0

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 70
NWS STORM PREDICTION CENTER NORMAN OK
140 PM CST THU FEB 21 2008

THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF

CENTRAL AND SOUTHWEST LOUISIANA
WILKINSON COUNTY MISSISSIPPI
SOUTHEASTERN TEXAS
COASTAL WATERS

EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 140 PM UNTIL
900 PM CST.

TORNADOES…HAIL TO 1.5 INCHES IN DIAMETER…THUNDERSTORM WIND
GUSTS TO 70 MPH…AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
AREAS.

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 65 STATUTE
MILES NORTH AND SOUTH OF A LINE FROM 30 MILES WEST OF HUNTSVILLE
TEXAS TO 20 MILES SOUTHEAST OF BATON ROUGE LOUISIANA. FOR A
COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE
UPDATE (WOUS64 KWNS WOU0).

REMEMBER…A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS.

DISCUSSION…THUNDERSTORMS WILL CONTINUE TO INTENSIFY/INCREASE
ACROSS SERN TX INTO SWRN/S-CENTRAL LA THROUGH THE AFTERNOON AS
CAPPING WEAKENS WITHIN VERY MOIST BOUNDARY LAYER. DEEP ASCENT WILL
ALSO INCREASE THROUGH THE DAY AHEAD OF STRONG MID/UPPER LEVEL TROUGH
NOW MOVING ACROSS THE SRN PLAINS. IN RESPONSE…A SURFACE LOW WILL
DEEPEN AND LIFT NEWD INTO CENTRAL LA THROUGH THE MID EVENING.
EFFECTIVE SHEAR REMAINS MORE THAN ADEQUATE FOR SUPERCELLS…WITH
SUFFICIENT LOW LEVEL SHEAR AND LOW LCL HEIGHTS FOR ADDITIONAL
TORNADO THREAT. ISOLATED DAMAGING WINDS AND LARGE HAIL ARE
ADDITIONAL HAZARDS.

AVIATION…TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
450. MEAN STORM MOTION VECTOR 25030.

…EVANS

Please note that paths are not to scale. They are rough estimations based off of NWS survey data.

If you find tornado information not currently included on this map, please send it to contact “at” tornadotonyDOTcom.