Short Wave Identification

[jgf]

I have read a few articles about identifying shortwaves, but always have trouble doing so.

 

Below, I have copied a portion of today's  (07:47 EDT 5/25) AFD from the Upton NY office, on Long Island:

 

First, for today, they say "deep layered ridging builds in" - i am pretty sure i see this in the upper level GFS charts  - it arrives from the SW

 

then, they say for thursday "deep layered ridging remains in control..., However a 700-500hpa shortwave passes over top of the ridge and through the area thursday afternoon"

 

Can somebody find upper level forecasts that illustrate the shortwave passing over the ridge?

 

i should note that in the foreast they say they slightly prefer the euro and the nam over the GFS, but I think it's just in the details - i think they are saying that the shortwave is present in all models.

 

 

in any case, i was looking at pivotal weather, as they have upper level forecasts from each model

 

i don't see the shortwave on thursday

 

thanks

 

000
FXUS61 KOKX 251147
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
747 AM EDT WED MAY 25 2016

.SYNOPSIS...
High pressure builds to the south, then southeast, through
tonight followed by a weak cold front crossing the area on
Thursday. This front then lifts north as a warm front Thursday
night, with high pressure building in behind the front through
Saturday night. A series of frontal boundaries then impact the
area from Sunday into Tuesday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Continued an SPS for patchy fog, locally dense at times, for
the Twin Forks of Long Island and portions of southern CT through
9 am. Looking at local web cams, it does seem to be improving
somewhat, however, given some of the recent observations, locally
dense fog is still occurring.

Otherwise, deep layered ridging builds in
today, with associated subsidence keeping cloud cover relatively
at bay, once any morning fog burns off, other than some passing
cirrus in the afternoon. It appears the subsidence should also be
strong enough to keep any convection at bay this afternoon over
the County Warning Area (CWA), so have gone with a dry forecast.

For highs today, a blend of mixing down from 825-775 hPa, per
BUFKIT soundings, NAM 2-meter temperatures, and a mixture of
MAV/ECS/MET guidance was used. Highs should be around 15 degrees
above normal. It would not be surprising if a location of two in
NE NJ, the Lower Hudson Valley and maybe even normally warmer
locations in NYC reached the 90 degree mark. The afternoon
seabreeze should prevent any record highs from being reached.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
Deep layered ridging remains in control tonight and Thursday. It
will be dry tonight, with only some high clouds around. However,
a 700-500 hPa shortwaves passes over the top of the ridge, and
through the area Thursday afternoon. This, coupled with surface
based CAPE of 5000-1000 J/kg, Showalter Indices from -2 to 2, and
20-25kt of Bulk shear over roughly the NW 2/5 of the CWA, warrants
slight chance to chance pops in that region.

It should be noted that the ECMWF suggests that there should be
sufficient subsidence under the ridge to keep things dry
throughout the area on Thursday. The GFS however suggests fairly
extensive convection over roughly the NW 2/5 of the CWA, with the
NAM somewhat in between (though closer to the ECMWF than the
GFS). Noting, that in addition to the passing shortwave, will also
have a cold front sinking south into the region. Based on this, it
appears there is enough forcing to warrant pops at this time.
However, there is still the potential for no precipitation at all
on Thursday.

[griteater]

You can see the weak shortwave with its trough axis centered over Erie, PA in the 2 images on the left (GFS model).  Upper left is at 500mb; lower left is at 700mb.

 

Four panel on PSU eWall is excellent for viewing:

http://mp1.met.psu.edu/~fxg1/AVN_12z/avnloopnew.html

http://mp1.met.psu.edu/~fxg1/ewall.html

[jgf]

it always amazes me that meteorologists find these tiny raster plots useful...

 

but i think i see it - did i get it right?

 

if you had to pick one level that is the best to check for them, what would it be? i have read 850...

 

[griteater]

it always amazes me that meteorologists find these tiny raster plots useful...

 

but i think i see it - did i get it right?

 

if you had to pick one level that is the best to check for them, what would it be? i have read 850...

Yes, your red line is the shortwave trough axis.  Shortwaves are most commonly referenced to the 500mb level.

 

The eWall maps are good for seeing loops of multiple levels of the atmosphere, all on one page (via the 4 panel)...but yes, they don't give you the 'blown-up' & detailed map of a single height level.

 

More info on this topic:

http://apollo.lsc.vsc.edu/classes/met130/notes/chapter12/long_short_waves.html

http://www.wxonline.info/topics/waves.html

http://www.atmo.arizona.edu/students/courselinks/fall12/atmo336/lectures/sec1/p500mb.html

[jgf]

so in today's AFD there is more discussion of shortwaves....

 

this time, there is something that i have seen before in text forecasts.., and wondered about.

 

in particular, they are discussing shortwaves that seem to be of a significantly shorter wavelength than the one we identified above - they talk about several of them moving through in a single day...

 

for today: "Shortwaves moving through today are progged to be weaker than they were 24hrs ago.."

 

and for saturday; "...no significant lift outside of weak mid-level shortwaves..."

 

so they are forecasting multiple shortwaves moving over the area in the next 24hrs - what is that based on?

 

If i wanted to be able to make that forecast.., where would i look for the evidence?

 

I have looked at the 700mb forecasts, but don't see multiple shortwaves

 

 

 

 

 

000
FXUS61 KOKX 271827
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
227 PM EDT FRI MAY 27 2016

.SYNOPSIS...
Bermuda High pressure will remain across the region through the
weekend. A cold front will pass through the area Monday into
Tuesday. High pressure returns for the middle of the week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Convection has fired well nw. Will need to keep an eye on western
zones, west of the Hudson, for possible shower and thunderstorm
development early. HRRR continues to develop convection, along
the seabreeze boundary. Will seabreeze boundary be enough to
break the cap. With increasing cape as the afternoon progresses,
coverage increases warranting chance pops.

The forecast remains on track.

Shortwaves moving through today are progged to be weaker than they
were 24 hours ago. No changes to temps at this time. 850 mb temps
and sea breeze progress should be close to those of yesterday, but
yesterday featured a mostly sunny sky for most of the day for most
locations. Will forecast high temps lower than what occurred
yesterday. Looks like clouds will be more numerous and more opaque
this time around. Have gone above a guidance blend for high
temps, especially across Long Island where guidance has been too
low during the past couple of days.

There is a moderate risk of rip current development at the Atlantic
beaches Today into this evening.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
An evening shower/thunderstorm is possible northwest of the city,
then with the loss of instability and only weak lift, dry
overnight.

For Saturday, still no significant source of lift outside of weak
mid level shortwaves, but SBCAPEs will be building once again away
from sea breezes. Again, will go with only slight chance to
chance pops, focused more toward the afternoon and away from areas
cooled by sea breezes.

Highs on Saturday should be warmer than on Friday with warmer temps
at the top of the mixed layer, and probably less cloud cover
overall. Again, needed to adjust a guidance blend upward to account
for the low bias as of late, especially over Long Island.

 

[griteater]

so in today's AFD there is more discussion of shortwaves....

 

this time, there is something that i have seen before in text forecasts.., and wondered about.

 

in particular, they are discussing shortwaves that seem to be of a significantly shorter wavelength than the one we identified above - they talk about several of them moving through in a single day...

 

for today: "Shortwaves moving through today are progged to be weaker than they were 24hrs ago.."

 

and for saturday; "...no significant lift outside of weak mid-level shortwaves..."

 

so they are forecasting multiple shortwaves moving over the area in the next 24hrs - what is that based on?

 

If i wanted to be able to make that forecast.., where would i look for the evidence?

 

I have looked at the 700mb forecasts, but don't see multiple shortwaves

In this case, there is ridging building in today at 500mb in your area.  If you look at the 700mb Relative Humidity charts, you can see an area of increased moisture working over the top of the ridge from NY/PA into S New England today...but it's very, very subtle.  A minor ripple as opposed to a "shortwave"

 

Go here and take a look at the GFS/Mid-Atlantic sector/700mb/Relative Humidity:

http://weather.cod.edu/forecast/

[jgf]

I see the RH surge that you mention

 

But, if we define a shortwave as a trough in the pressure levels between say 850 and 500mb.., i certainly don't see that there are several passing over my region...

 

So.., is it the case that the forecaster who wrote the AFD saw the RH surge.., and just inferred that there must be several shortwaves (troughs in the pressure surfaces) passing over my region.., even though they are not resolved by the models?

 

I am just trying to nail down the reason for that forecast

[griteater]

Those are good questions.  It's possible the forecaster was using a higher resolution model (e.g. HRRR) which is more capable of resolving the smaller scale features.  One thing of note is that weak shortwaves or ripples in the flow are more likely to influence the sensible weather during the warm season than during the cool season...that is, when abundant low level warmth and moisture are present, a weak shortwave can assist in providing the necessary forcing/lift for showers and storms....whereas during the cool season, such a feature may only lead to an increase in cloud cover.

[jgf]

I have looked at the HRRR

 

i find it hard to use it for looking at pressure surfaces.., because it seems susceptible to contouring artifacts

 

if you look at HRRR CONUS plots, they don't resolve small features

 

if you look at regional plots, there seem to be spurious structures in individual contour lines that aren't reflected in adjacent lines

 

I have also downloaded the HRRR grib files.., and then my own software does the contouring.., but i have the same issues.

 

so, no, i haven't been able to identify small scale shortwaves in the HRRR

 

The HRRR has been unavailable more than it's been available lately

[ohleary]

I have looked at the HRRR

 

i find it hard to use it for looking at pressure surfaces.., because it seems susceptible to contouring artifacts

 

if you look at HRRR CONUS plots, they don't resolve small features

 

if you look at regional plots, there seem to be spurious structures in individual contour lines that aren't reflected in adjacent lines

 

I have also downloaded the HRRR grib files.., and then my own software does the contouring.., but i have the same issues.

 

so, no, i haven't been able to identify small scale shortwaves in the HRRR

 

The HRRR has been unavailable more than it's been available lately

 

The HRRR is available every hour of every day.  Are you looking at the ESRL site?  Because yeah, it's not always there.

 

http://mag.ncep.noaa.gov/model-guidance-model-area.php

[jgf]

The HRRR is available every hour of every day.  Are you looking at the ESRL site?  Because yeah, it's not always there.

 

http://mag.ncep.noaa.gov/model-guidance-model-area.php

 

yes - i usually go to the ESRL site for HRRR graphics because i need more detail than is on the NCEP site

 

but you are right - i see that even though it is not on the ESRL site, the model is still available

 

i like to look at the OKX sub region on the ESRL site

 

otherwise I download the gribs from NOMADS, and can view the model in it's full resolution - i see the gribs are available today, even though there is nothing on the ESRL site.

 

I guess i don't really understand how such low res graphics as the ones on the NCEP HRRR site are that useful to you guys, but i guess they must be...

 

my main interest is wind.., and its variation over short distances, so  even the OKX graphic really isn't that great

 

my main problem is that NOMADS is quite cumbersome to use - i have to select and download a separate file for each forecast time

 

if i was more clever, i could probably write a script to download the HRRR grib for all the forecast times, and for the region and variables of interest to me

[jgf]

Quote

000
FXUS61 KOKX 101444
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1044 AM EDT WED AUG 10 2016

.SYNOPSIS...
Bermuda high pressure will remain across the Western Atlantic
through the weekend. A cold front approaches on Monday and moves
across Monday night into Tuesday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
The area will remain under the influence of Bermuda high pressure
through today with ridging over the northeast. A weak shortwave
and associated convective complex were moving through the ridge
and sagging into the forecast area. Additional convective vort
maxima will move through the ridge today, increasing the chance of
showers and thunderstorms. These storms will track along the
periphery of the ridge with the higher chances of precipitation
across the lower Hudson Valley into southern Connecticut. There
will be little shear and steering flow, with increasing isentropic
lift, along with diurnal instability. With a deep layered moisture
influx from the Gulf of Mexico there is the potential for areas of
heavy rainfall as the storms will also be slow moving.

 

so that's the Upton AFD for this afternoon

another shortwave forecast..., but I struggle to see it.., i see the high.., not sure i would really say new england is under a ridge though...

i do see a long wavelength, small amplitude curve in the contour that passes just N of PA

is that it?

 

 

 

[ohleary]

Probably need to look lower. 850mb, look over NY:

 

 

700mb: pretty evident here, see the RH just upstream of the shortwave in New England: