Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260208_1200
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 02/08 12Z 0.04 3420  75  65 -21 0.00
Sun 02/08 13Z 0.04 3424  72  59 -19 0.00
Sun 02/08 14Z 0.03 3425  70  62 -19 0.00
Sun 02/08 15Z 0.03 3425  69  65 -19 0.00
Sun 02/08 16Z 0.03 3426  69  65 -18 0.00
Sun 02/08 18Z 0.03 3427  64  31 -16 0.00
Sun 02/08 19Z 0.03 3426  64  20 -15 0.00
Sun 02/08 20Z 0.03 3426  65  43 -15 0.00
Sun 02/08 21Z 0.03 3426  65  52 -14 0.00
Sun 02/08 22Z 0.02 3427  61  42 -13 0.00
Sun 02/08 23Z 0.02 3428  56  45 -12 0.00
Mon 02/09 00Z 0.02 3428  53  51 -12 0.00
Mon 02/09 01Z 0.02 3429  51  51 -12 0.00
Mon 02/09 02Z 0.02 3429  50  45 -11 0.00
Mon 02/09 03Z 0.05 3429  56  41 -11 0.00
Mon 02/09 04Z 0.07 3429  60  38 -11 0.00
Mon 02/09 05Z 0.09 3330  60  33 -12 0.00
Mon 02/09 06Z 0.11 3331  59  30 -12 0.00
Mon 02/09 07Z 0.12 3332  59  28 -12 0.00
Mon 02/09 08Z 0.10 3332  62  26 -12 0.00
Mon 02/09 09Z 0.10 3333  64  25 -12 0.00
Mon 02/09 10Z 0.09 3333  64  21 -12 0.00
Mon 02/09 11Z 0.07 3433  62  16 -11 0.00
Mon 02/09 12Z 0.07 3433  60  14 -11 0.00
Mon 02/09 13Z 0.06 3433  59  12 -11 0.00
Mon 02/09 14Z 0.05 3433  56  15 -11 0.00
Mon 02/09 15Z 0.03 3432  52  28 -11 0.00
Mon 02/09 16Z 0.03 3430  52  58 -10 0.00
Mon 02/09 17Z 0.04 3428  51  69 -11 0.00
Mon 02/09 18Z 0.08 3427  50  65 -11 0.00
Mon 02/09 19Z 0.09 3326  46  57 -10 0.00
Mon 02/09 20Z 0.10 3325  45  51 -10 0.00
Mon 02/09 21Z 0.11 3325  41  50  -9 0.00
Mon 02/09 22Z 0.10 3325  38  54  -8 0.00
Mon 02/09 23Z 0.07 3425  35  50  -8 0.00
Tue 02/10 00Z 0.08 3325  35  42  -8 0.00
Tue 02/10 01Z 0.07 3425  35  33  -8 0.00
Tue 02/10 02Z 0.07 3324  33  35  -8 0.00
Tue 02/10 03Z 0.07 3322  31  43  -8 0.00
Tue 02/10 04Z 0.06 3420  30  60  -8 0.00
Tue 02/10 05Z 0.06 3418  31  73  -8 0.00
Tue 02/10 06Z 0.05 3416  35  77  -7 0.00
Tue 02/10 07Z 0.06 3315  38  80  -7 0.00
Tue 02/10 08Z 0.10 3215  39  82  -8 0.00
Tue 02/10 09Z 0.07 3314  41  77  -7 0.00
Tue 02/10 10Z 0.10 3213  42  78  -7 0.00
Tue 02/10 11Z 0.08 3210  46  75  -7 0.00
Tue 02/10 12Z 0.09 3208  47  71  -7 0.00
Tue 02/10 13Z 0.10 3007  48  76  -7 0.00
Tue 02/10 14Z 0.11 2806  49  77  -7 0.00
Tue 02/10 15Z 0.10 2504  49  76  -7 0.00
Tue 02/10 16Z 0.13 2306  51  78  -7 0.00
Tue 02/10 17Z 0.12 2106  54  76  -6 0.00
Tue 02/10 18Z 0.12 2008  56  69  -6 0.00
Tue 02/10 19Z 0.04 1710  54  65  -6 0.00
Tue 02/10 20Z 0.07 1812  56  92  -6 0.00
Tue 02/10 21Z 0.12 1813  58  92  -7 0.00
Tue 02/10 22Z 0.04 1713  88  93  -9 0.00
Tue 02/10 23Z 0.05 1620  92  95  -8 0.01

Run total areal avg QPF for the Central_Greens is: 0.01 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1