Jot Ross wrote:

Some reasons for higher temp max variability...

(1) Daytime, horizontal wind...Marine flow vs. land flow and in Eastern MA,
warming downslope flow. Wind tends to calm at night and these influences
are often minimized.

(2) ³Vertical wind² will develop if, as or when temperature inversion is
broken.

(3) As we progress later into Spring and into summer, those of us who
record temp/dewpoint will note that almost always temp is at or near
dewpoint at time of minimum temp. In other words, the relative humidity
tends to be close to 100% at time of minimum temp (often 5 - 6 AM).

That seems to be true at most locations, but does not seem to necessarily be
so at mine. For example, MPO had a minimum of 53 last night :

KMPO 080453Z AUTO VRB03KT 6SM BR FEW085 17/14 A3023 RMK AO2 SLP228 T01670144
402440117=
KMPO 080553Z AUTO VRB03KT 6SM BR BKN090 16/14 A3023 RMK AO2 SLP227 T01560144
10206 20156 50005=
KMPO 080653Z AUTO VRB03KT 5SM BR CLR 15/14 A3024 RMK AO2 SLP231 T01500144=
KMPO 080753Z AUTO 00000KT 3SM BR CLR 13/13 A3024 RMK AO2 SLP233 T01330133=
KMPO 080853Z AUTO 00000KT 1 3/4SM BR FEW085 12/12 A3024 RMK AO2 SLP234
T01220122 50004=
KMPO 080953Z AUTO 00000KT 2 1/2SM BR FEW090 14/14 A3025 RMK AO2 SLP236
T01440139=
KMPO 081053Z AUTO 00000KT 2 1/2SM BR FEW090 16/15 A3025 RMK AO2 SLP237 P0001
T01560150=
KMPO 081153Z AUTO 26005KT 6SM HZ FEW100 19/16 A3026 RMK AO2 SLP239 60001 70001
T01890161 10189 20117 51008=

and my mercury min/max thermomter shows a minimum of 60. As can be seen
in the METAR's, they went calm and cooled a bit past the dewpoint, 3 miles
away and 300 feet lower, we didn't. Yet I don't measure dewpoint, so I
cannot say how close our dewpoint was to 60.

Most people would refer to your "vertical wind" simply as "convection".
Just as the dewpoint is a quasi-limit for nighttime temperature (it does
sometimes decrease past the dewpoint though), the dry adiabatic lapse also
limits daytime temperature (though it can be superadiabatic). Just as the
dewpoint can change, so too can temperatures aloft. Heating can continue
dry adiabatically indefinitely, but the more so it does, the deeper the
layer which must be adiabatically heated to increase temperature the same
amount - why the temperature increases rapidly during morning and then
slowly midday-afternoon, which is very noticeable here in the Poconos. The
ESE-facing slope absorbs more sunshine than other locations during morning
then it isn't long before (because of elevation) heating must overcome
the dry adiabatic lapse rate thru to top of the boundary layer. Note 10
AM temperatures here today :


REGIONAL WEATHER ROUNDUP
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1000 AM EDT TUE JUN 8 2004

NJZ001014-081500-
NORTHERN NEW JERSEY
CITY SKY/WX TMP DP RH WIND PRES REMARKS
SUSSEX SUNNY 74 64 71 VRB3 30.23R
ANDOVER N/A 75 62 64 VRB6 30.23S
MORRISTOWN SUNNY 81 66 61 W9 30.23S HAZE
NEWARK MOSUNNY 79 64 60 W8 30.20F
TETERBORO SUNNY 79 65 62 VRB6 30.19S HAZE
CALDWELL SUNNY 76 65 68 VRB5 30.21F HAZE
SOMERVILLE SUNNY 77 65 66 VRB5 30.20F
ALLAIRE* SUNNY 75 66 73 W8 30.22F

PAZ043-044-047-054-055-060062-066071-081500-
EASTERN PENNSYLVANIA
CITY SKY/WX TMP DP RH WIND PRES REMARKS
PHILADELPHIA MOSUNNY 74 66 76 SW8 30.24F HAZE
NORTH PHILA SUNNY 78 66 66 SW8 30.23F
BLUE BELL* FAIR 79 64 61 SW7 30.22F
DOYLESTOWN SUNNY 76 65 68 VRB6 30.22F
POTTSTOWN SUNNY 75 67 76 VRB5 30.24F
LANCASTER MOSUNNY 70 59 68 VRB3 30.25F HAZE
READING SUNNY 72 66 81 CALM 30.21F HAZE
ALLENTOWN SUNNY 75 64 68 W7 30.23F HAZE
MOUNT POCONO MOSUNNY 73 61 65 VRB7 30.28R
WILKES BARRE SUNNY 73 61 65 VRB6 30.24S


Mount Pocono was nearly the same as Philadelphia, Allentown, & Wilkes-Barre.
I'll post the maximum temperatures later. 81 at Morristown - wow !

So I was reluctant to answer your question because though I expected you
to mention dewpoint limiting temperature, there also is a limit of sorts
(though generally not as much of one) for daytime maximum. The one about
ocean/land winds is something which did not cross my mind.


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