Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260208_1800
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 18Z 0.03 3422  71  23 -17 0.00
Sun 02/08 19Z 0.04 3425  68  27 -16 0.00
Sun 02/08 20Z 0.05 3427  68  40 -15 0.00
Sun 02/08 21Z 0.06 3428  63  52 -14 0.00
Sun 02/08 22Z 0.06 3428  61  57 -14 0.00
Sun 02/08 23Z 0.05 3429  59  58 -13 0.00
Mon 02/09 00Z 0.03 3430  56  56 -13 0.00
Mon 02/09 01Z 0.03 3431  54  53 -12 0.00
Mon 02/09 02Z 0.02 3430  57  40 -12 0.00
Mon 02/09 03Z 0.04 3429  61  35 -12 0.00
Mon 02/09 04Z 0.07 3428  62  34 -12 0.00
Mon 02/09 05Z 0.09 3328  64  36 -12 0.00
Mon 02/09 06Z 0.11 3329  65  33 -12 0.00
Mon 02/09 07Z 0.12 3331  64  31 -12 0.00
Mon 02/09 08Z 0.13 3332  66  29 -12 0.00
Mon 02/09 09Z 0.12 3333  64  27 -12 0.00
Mon 02/09 10Z 0.11 3333  62  23 -12 0.00
Mon 02/09 11Z 0.10 3334  59  18 -12 0.00
Mon 02/09 12Z 0.08 3434  56  13 -12 0.00
Mon 02/09 13Z 0.07 3434  53  11 -12 0.00
Mon 02/09 14Z 0.07 3432  51  12 -11 0.00
Mon 02/09 15Z 0.07 3431  49  23 -11 0.00
Mon 02/09 16Z 0.06 3429  49  49 -11 0.00
Mon 02/09 17Z 0.08 3428  48  58 -11 0.00
Mon 02/09 18Z 0.11 3327  47  75 -11 0.00
Mon 02/09 19Z 0.11 3325  46  66 -11 0.00
Mon 02/09 20Z 0.11 3324  40  46 -10 0.00
Mon 02/09 21Z 0.13 3324  36  43  -9 0.00
Mon 02/09 22Z 0.12 3324  33  47  -8 0.00
Mon 02/09 23Z 0.10 3324  30  55  -8 0.00
Tue 02/10 00Z 0.12 3324  33  53  -8 0.00
Tue 02/10 01Z 0.10 3323  31  55  -8 0.00
Tue 02/10 02Z 0.09 3322  29  60  -8 0.00
Tue 02/10 03Z 0.08 3321  30  68  -8 0.00
Tue 02/10 04Z 0.08 3320  34  74  -8 0.00
Tue 02/10 05Z 0.09 3319  37  86  -8 0.00
Tue 02/10 07Z 0.08 3316  40  82  -8 0.00
Tue 02/10 08Z 0.09 3314  40  77  -7 0.00
Tue 02/10 09Z 0.10 3212  36  75  -8 0.00
Tue 02/10 10Z 0.10 3210  36  72  -8 0.00
Tue 02/10 11Z 0.13 3008  37  73  -8 0.00
Tue 02/10 12Z 0.11 2906  45  64  -7 0.00
Tue 02/10 13Z 0.11 2705  51  60  -7 0.00
Tue 02/10 14Z 0.13 2505  57  58  -7 0.00
Tue 02/10 15Z 0.11 2205  64  57  -7 0.00
Tue 02/10 16Z 0.11 2106  65  58  -7 0.00
Tue 02/10 17Z 0.12 2009  61  61  -6 0.00
Tue 02/10 18Z 0.14 1911  51  60  -6 0.00
Tue 02/10 19Z 0.13 1913  44  62  -6 0.00
Tue 02/10 20Z 0.10 1814  47  89  -6 0.00
Tue 02/10 21Z 0.18 1915  56  93  -7 0.00
Tue 02/10 22Z 0.04 1716  91  97  -8 0.00
Tue 02/10 23Z 0.07 1720  93  94  -6 0.02
Wed 02/11 00Z 0.16 1822  94  93  -7 0.06
Wed 02/11 01Z 0.32 1921  94  96  -9 0.06
Wed 02/11 02Z 0.41 2119  95  95  -9 0.05
Wed 02/11 03Z 0.47 2218  96  95  -8 0.05
Wed 02/11 04Z 0.47 2317  97  89  -8 0.04

Run total areal avg QPF for the Central_Greens is: 0.28 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