Friday Map Discussion: 13 April 2007

All attachments: http://www.atmos.albany.edu/student/heathera/mapdisc_04-13-07/

(with Paul Roundy’s response appended below)

Hi Folks,

The "Friday the 13th" map discussion for 13 Apr'07 featured (with apologies to Jack Nicholson) a "shining" example of weather run amok and where should we start first questions.

Given all the moaning and groaning about where is spring (it was back in Jan when it was a record-breaking 70 F for the first and only time this year) and woe is is, we opened with a discussion of recent height/temperature anomaly patterns around the NH. The attached 300 Z/Z' and 850 T/T' maps for 4-11 Ap'07 make the following points:

1) Much of the US east of the Rockies was dominated by the biggest negative 850 temperature anomalies anywhere in the NH.....confirming woe is us. A closer look shows that the cold-air factories over northeastern Asia and northwestern Canada are a

little short on "product." The sun will win eventually.

2) An even closer look at the 850 hPa T/T' pattern shows that most of the continental areas of the NH were dominated by positive temperature anomalies, confirming that the short-term climate dice still have more red faces than blue faces. I don't think that there

are too many complaints that it's too cool from the Sahara eastward across almost all of Asia.

2) The 300 hPa height pattern is dominated by an unusually deep trough over eastern North America and an anomalously elongated and strengthened Pacific jet that appears to be shifted equatorward and eastward of its climatological position. Persistent storminess over

the eastern pacific in the exit-region of this time-mean 300 hPa jet has reinforced the western North America ridge and has helped to lock in the cold air over central and eastern North America.

3) The wave-like 300 hPa height anomaly patterns around the NH raises the question as to whether energy has been propagating at the group velocity along great circles from anomalous tropical heating sources. A search for possible tropical heating anomaly smoking guns

proved unsuccessful. Enlightenment from the remote outposts of map would be appreciated on this question.

The next phase of map discussion dealt with the severe weather that was just beginning in TX as we were speaking. It was also recognized that the disturbance responsible for the expected severe weather that would continue overnight Fri into Sat and Sat night

was also going to be the main player in the already overly hyped Sun/Mon East Coast nor'easter. Lots of uncertainty as to where (and beginning at what elevation) any heavy snow will fall. Lots of certainty that significant air travel disruptions would be likely on Sun

along the East Coast due to coastal heavy rains and high winds. Given that this week has been spring break for many school districts and that flights are booked solid for tomorrow, look for another potential airline mess with lots of "happy" stranded travelers jamming

airports.

A few possible research issues..........

The undulating behavior of the approximately east-west thermal boundary across TX eastward to AR/LA yesterday was of interest. This boundary served as one focus for severe weather, especially where it intersected a diffuse dryline. Plotted surface maps, obtained

from NCAR/RAP, centered on this region are attached for 21Z/13, and 00Z, 03Z and 06Z/14. Similarly, surface potential temperature maps derived from U-Albany (www.atmos.albany.edu/deas/data.html; look under surface maps) are attached for 20Z, 23Z/13 and 03Z, 06Z/14. A TX/OK regional base reflectivity image for 0000 UTC 14 Apr'07 is also attached. Features of interest include:

1) Strongly backed surface SE winds in the Dallas-Fort Worth, TX, area just to the south of the east-west oriented warm front residing in the Red River Valley of the South during the mid-to-late afternoon hours on the 13th. Severe weather was reported in the DFW area at

this time.

2) A NNE-SSW oriented wind shift line across southern OK on the cold side of east-west oriented warm-front boundary. This wind shift line moves eastward across southern OK in the 4 h ending 00Z/14. The wind shift line separated northerly and easterly air flows and

coincided closely with a line of convective storms that extended from the warm air into the cold air (see 00Z/14 regional radar reflectivity image). It likely marks the western edge of the plume of low-level warm, moist air that is overriding the surface warm front.

3. The formation of dual mesoscale circulation features along the east-west oriented thermal boundary. The surface theta map for 23Z/13 shows a clear cyclonic circulation center along the southern margins of the TX panhandle. This cyclonic circulation coincides nicely

with the apex of the thermal ridge. A second mesoscale cyclonic circulation center lies along the thermal boundary just to the northwest of the Dallas metroplex. This mesoscale feature is clearly associated with the backed winds in the Dallas-Fort Worth area, but unlike the mesoscale circulation center further to the west, it is located to the west of the apex of the thermal ridge. The eastern mesoscale circulation center appears to be tied to the region of lower theta advection (positive potential vorticity (PV) advection) on the dynamic tropopause (DT) as seen on the DT/theta image for 00Z/14. The western mesoscale circulation center is situated beneath the leading part of the PV hook. Subsequent to 00Z/14 the western mesoscale circulation center weakens while the eastern center advances eastward toward extreme northeastern Texas.

4) Subsequent to 00Z/14 the east-west warm-front boundary across northern Louisiana (LA) exhibited oscillatory behavior, especially at Reston (RSN). Note the decrease of temperature from 21 to 18 C 0021Z/14 as winds shifted from light SE to light northerly. Subsequently

a 7 C rise from 16 C to 23 C was observed 0241Z/14 and 0301Z/14 as a gusty, moist SSE flow arrived. The period between 04121Z/14 and 0521Z/14 featured two more 6-7 C temperature (and dew point) swings as the warm frontal boundary continue to oscillate across the RSN area. The surface theta maps suggest that the theta boundary remain somewhat displaced to the south across northwestern LA as compared to further west and west. At issue is why. A question arises as to whether as to whether weak cold air damming to the east of the

Ouachita and Boston mountains in Arkansas may have helped to deflect stable, low-level cool air further southward into northern LA.

As to the coastal storm tomorrow, it should be monitored for any signs of unusual behavior, particularly with regard to any potential convective influences in the warm sector and possible diabatically influenced ridge building downstream aloft.

Lance

METAR reports from Ruston (RSN), LA: 2100 UTC 13 April through 0900 UTC 14 April 2007

KRSN 140900Z AUTO 20005KT 10SM BKN008 BKN022 OVC090 16/16 A2975 RMK AO2 LTG DSNT NE THRU S

KRSN 140840Z AUTO 20003KT 10SM SCT006 SCT010 BKN100 16/16 A2971 RMK AO2 LTG DSNT NE THRU SE

KRSN 140820Z AUTO 26003KT 10SM VCTS SCT008 BKN016 OVC110 16/16 A2969 RMK AO2 LTG DSNT NE THRU S

KRSN 140800Z AUTO 24003KT 10SM VCTS BKN008 BKN020 OVC040 16/16 A2969 RMK AO2 LTG DSNT NE THRU S

KRSN 140740Z AUTO 18005KT 5SM TSRA SCT006 BKN020 OVC043 16/16 A2968 RMK AO2 P0071 LTG DSNT ALQS

KRSN 140721Z AUTO 25010KT 2SM +TSRA BKN010 BKN018 OVC032 15/15 A2972 RMK AO2 P0025 LTG DSNT ALQS

KRSN 140703Z AUTO 26005KT 5SM -TSRA SCT004 BKN012 OVC036 14/14 A2970 RMK AO2 LTG DSNT ALQS P0002

KRSN 140700Z AUTO 33006KT 4SM TSRA SCT004 BKN008 OVC036 13/13 A2970 RMK AO2 P0001 LTG DSNT ALQS

KRSN 140621Z AUTO 28011KT 10SM -TSRA SCT003 OVC008 13/13 A2970 RMK AO2 P0001 LTG DSNT ALQS

KRSN 140601Z AUTO 01003KT 5SM -TSRA SCT003 BKN008 OVC019 14/13 A2966 RMK AO2 P0001 LTG DSNT ALQS

KRSN 140541Z AUTO 33003KT 4SM -TSRA OVC017 15/14 A2966 RMK AO2 LTG DSNT ALQS

KRSN 140521Z AUTO 32005KT 7SM -VCTSRA BKN017 OVC023 15/13 A2967 RMK AO2 LTG DSNT ALQS

KRSN 140501Z AUTO 20015G19KT 10SM VCTS OVC021 22/20 A2967 RMK AO2 LTG DSNT ALQS

KRSN 140441Z AUTO 02005KT 10SM VCTS OVC021 16/14 A2968 RMK AO2 LTG DSNT ALQS

KRSN 140421Z AUTO 22004G18KT 10SM BKN021 OVC027 23/19 A2969 RMK AO2 LTG DSNT W THRU NE

KRSN 140401Z AUTO 19015G22KT 10SM VCTS SCT023 BKN027 OVC049 23/19 A2968 RMK AO2 LTG DSNT W THRU NE

KRSN 140341Z AUTO 17022G30KT 10SM VCTS BKN025 OVC033 23/19 A2966 RMK AO2 LTG DSNT NW THRU NE

KRSN 140321Z AUTO 18016G22KT 10SM BKN025 OVC031 23/18 A2967 RMK AO2 LTG DSNT SW THRU N

KRSN 140301Z AUTO 17017G23KT 10SM VCTS OVC030 23/18 A2967 RMK AO2 LTG DSNT W THRU NE

KRSN 140241Z AUTO 00000KT 10SM VCTS OVC030 16/13 A2969 RMK AO2 LTG DSNT N AND NW

KRSN 140221Z AUTO 00000KT 10SM VCTS OVC032 16/12 A2970 RMK AO2 LTG DSNT NW THRU NE

KRSN 140201Z AUTO 00000KT 10SM OVC032 15/13 A2970 RMK AO2 LTG DSNT N AND NW

KRSN 140141Z AUTO 36003KT 10SM OVC036 15/13 A2971 RMK AO2 LTG DSNT W THRU NE

KRSN 140121Z AUTO 36005KT 10SM TS OVC038 16/13 A2971 RMK AO2 LTG DSNT NW THRU NE

KRSN 140101Z AUTO 36003KT 10SM -TSRA BKN040 OVC046 16/14 A2971 RMK AO2 LTG DSNT ALQS

KRSN 140041Z AUTO 02005KT 10SM VCTS BKN043 BKN049 OVC060 18/16 A2972 RMK AO2 LTG DSNT ALQS

KRSN 140021Z AUTO 35004KT 10SM VCTS SCT048 OVC060 18/17 A2973 RMK AO2 LTG DSNT NW THRU NE

KRSN 140001Z AUTO 15004KT 10SM SCT047 OVC060 21/16 A2973 RMK AO2 LTG DSNT W THRU N

KRSN 132341Z AUTO 11004KT 10SM BKN060 OVC070 20/17 A2973 RMK AO2 LTG DSNT N AND NW

KRSN 132321Z AUTO 00000KT 10SM SCT050 OVC080 20/16 A2975 RMK AO2 LTG DSNT W THRU NE

KRSN 132301Z AUTO 11003KT 10SM VCTS OVC080 19/16 A2976 RMK AO2 LTG DSNT N AND NW

KRSN 132241Z AUTO 00000KT 7SM -VCTSRA OVC080 21/16 A2977 RMK AO2 P0002 LTG DSNT ALQS

KRSN 132221Z AUTO 11003KT 10SM VCTS SCT050 OVC070 22/12 A2977 RMK AO2 LTG DSNT W THRU NE

KRSN 132201Z AUTO 09004KT 10SM -TSRA SCT050 OVC070 22/12 A2978 RMK AO2 LTG DSNT W THRU NE

KRSN 132141Z AUTO 10006KT 10SM TS OVC070 23/11 A2979 RMK AO2 LTG DSNT SW THRU N

KRSN 132121Z AUTO 13004KT 10SM BKN070 OVC080 23/10 A2983 RMK AO2 LTG DSNT NW

KRSN 132101Z AUTO 09003KT 10SM OVC060 23/11 A2984 RMK AO2

KRSN 132041Z AUTO 09005KT 10SM OVC060 23/10 A2985 RMK AO2 LTG DSNT NW

Hi, Lance and All. . . Although the tropical connection was difficult for

me to make during the map discussion, we did establish that there was a

westerly wind burst event and intense moist deep convection across the

equatorial West Pacific during the last few days of March and the first

week of April. I attached a pdf including two figures, both extracted

from CPC discussions. I added some crude notes to their figures. The top

panel shows OLR anomalies, with active convection suggested in cool

colors. The region of active convection associated with the westerly wind

burst is circled and labeled "Primary convective region". Although I do

not plot surface winds, westerly winds were located with the active

convection on the equator, with cyclonic gyres at the surface to the north

and south of the equator. The bottom panel shows 200 hPa wind anomalies.

Notice the large anticyclonic gyres to the north and south of the deep

convection. I drew a crude curve where we might expect the Rossby wave

train response. Interpretation is limited here because the figure does

not extend far enough north, but there does appear to be a wave train.

Please do not read too much into this figure as my plotted interpretation

is quite crude! Something else to consider is the influence of the deep

convective event at the same time on the north of South America.

Southwesterly outflow from that convection is evident on the bottom

figure.

For a more solid link to the West Pacific tropical connection, see the

animation of 200 hPa height at:

http://www.cpc.noaa.gov/products/intraseasonal/z200anim.shtml

which shows a ridge building event timed well with the deep convection and

the surface westerly wind burst, beginning to the east of Asia around 30

March and extending rapidly to the Arctic circle. Surely that event

modulated the development of our present highly amplified upper level

pattern. Thoughts?

Paul