Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260614_0600
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 06/14 06Z 0.53 2414  70  65  13 0.00
Sun 06/14 07Z 0.68 2418  67  66  14 0.00
Sun 06/14 08Z 0.71 2420  69  66  14 0.00
Sun 06/14 09Z 0.77 2323  80  67  14 0.00
Sun 06/14 10Z 0.78 2326  77  70  14 0.00
Sun 06/14 11Z 0.77 2426  75  62  14 0.00
Sun 06/14 12Z 0.75 2424  80  40  13 0.00
Sun 06/14 13Z 0.77 2522  87  34  13 0.00
Sun 06/14 14Z 0.74 2518  86  30  13 0.00
Sun 06/14 15Z 1.04 2416  84  41  13 0.00
Sun 06/14 16Z 2.54 2216  84  53  14 0.00
Sun 06/14 17Z 1.40 2118  82  67  14 0.00
Sun 06/14 18Z 1.52 2023  81  37  14 0.00
Sun 06/14 19Z 3.18 2123  76  32  15 0.00
Sun 06/14 20Z 3.53 2221  80  44  16 0.07
Sun 06/14 21Z 3.40 2119  81  63  16 0.01
Sun 06/14 22Z 1.06 2122  86  54  16 0.04
Sun 06/14 23Z 0.78 2121  78  48  16 0.09
Mon 06/15 00Z 0.56 2021  77  51  16 0.03
Mon 06/15 01Z 0.52 1925  78  65  16 0.05
Mon 06/15 02Z 0.59 1927  87  77  15 0.12
Mon 06/15 03Z 0.59 2028  93  84  15 0.20
Mon 06/15 04Z 0.98 2233  95  86  14 0.40
Mon 06/15 05Z 0.77 2226  93  89  13 0.20
Mon 06/15 06Z 0.53 2123  96  93  13 0.18
Mon 06/15 07Z 0.48 2219  99  96  12 0.44
Mon 06/15 08Z 0.53 2817  99  96  11 0.18
Mon 06/15 09Z 0.36 3121  96  89  10 0.06
Mon 06/15 10Z 0.47 3122  94  71   9 0.01
Mon 06/15 11Z 0.47 3121  93  54   9 0.01
Mon 06/15 12Z 0.50 3020  92  30   8 0.01
Mon 06/15 13Z 0.59 3021  92  19   7 0.01
Mon 06/15 14Z 0.68 3019  90  20   7 0.01
Mon 06/15 15Z 1.21 3018  92  15   6 0.01
Mon 06/15 16Z 1.76 3018  92  14   6 0.01
Mon 06/15 17Z 2.85 3016  89  12   6 0.00
Mon 06/15 18Z 4.20 3014  89  13   6 0.00
Mon 06/15 19Z 3.36 2913  89  15   7 0.00
Mon 06/15 20Z 2.83 2913  91  17   6 0.00
Mon 06/15 21Z 2.39 2915  89  20   6 0.00
Mon 06/15 22Z 1.73 2916  89  20   6 0.00
Mon 06/15 23Z 1.24 2917  91  19   6 0.00
Tue 06/16 00Z 1.01 2919  93  14   6 0.00
Tue 06/16 01Z 0.80 2921  92  13   6 0.00
Tue 06/16 02Z 0.60 3021  94  10   6 0.00
Tue 06/16 03Z 0.61 3022  94   8   5 0.01
Tue 06/16 04Z 0.50 3121  94   6   5 0.01
Tue 06/16 05Z 0.43 3121  93   4   5 0.00
Tue 06/16 06Z 0.35 3120  92   3   5 0.00
Tue 06/16 07Z 0.29 3219  91   2   5 0.00
Tue 06/16 08Z 0.28 3217  91   3   5 0.00
Tue 06/16 09Z 0.24 3215  90   2   5 0.00
Tue 06/16 10Z 0.23 3113  90   3   5 0.00
Tue 06/16 11Z 0.19 3111  90   9   5 0.00
Tue 06/16 12Z 0.17 3109  89  13   5 0.00
Tue 06/16 13Z 0.15 3006  87  13   5 0.00
Tue 06/16 14Z 0.19 2705  86  20   5 0.00
Tue 06/16 15Z 0.40 2605  85  32   5 0.00
Tue 06/16 16Z 1.18 2505  82  39   5 0.00
Tue 06/16 17Z 1.63 2505  76  41   6 0.00

Run total areal avg QPF for the Central_Greens is: 2.16 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