Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260119_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)
=== ===== === ==== ==== === === === ====
Mon 01/19 18Z 6.75 2313  89  75 -14 0.00
Mon 01/19 19Z 5.51 2316  89  72 -14 0.00
Mon 01/19 20Z 4.77 2320  91  80 -14 0.00
Mon 01/19 21Z 2.28 2324  92  75 -14 0.00
Mon 01/19 22Z 3.12 2426  90  70 -14 0.01
Mon 01/19 23Z 1.96 2427  86  46 -14 0.00
Tue 01/20 00Z 1.72 2428  88  54 -14 0.00
Tue 01/20 01Z 2.34 2531  86  45 -15 0.00
Tue 01/20 02Z 2.71 2531  83  46 -15 0.00
Tue 01/20 03Z 4.27 2531  81  45 -16 0.00
Tue 01/20 04Z 4.04 2531  77  47 -17 0.00
Tue 01/20 05Z 2.66 2531  80  42 -17 0.00
Tue 01/20 06Z 1.24 2530  82  48 -16 0.00
Tue 01/20 07Z 1.45 2531  89  39 -17 0.00
Tue 01/20 08Z 1.38 2629  89  46 -18 0.00
Tue 01/20 09Z 1.42 2627  90  48 -18 0.00
Tue 01/20 10Z 1.71 2626  90  59 -18 0.00
Tue 01/20 11Z 2.17 2624  88  54 -19 0.00
Tue 01/20 12Z 2.08 2624  84  51 -19 0.00
Tue 01/20 13Z 1.82 2723  78  50 -20 0.00
Tue 01/20 14Z 2.93 2722  78  50 -20 0.00
Tue 01/20 15Z 5.59 2721  79  56 -21 0.01
Tue 01/20 16Z 10.13 2720  79  59 -21 0.00
Tue 01/20 17Z 11.72 2619  80  62 -21 0.00
Tue 01/20 18Z 11.00 2519  80  65 -20 0.00
Tue 01/20 19Z 12.38 2620  74  67 -20 0.00
Tue 01/20 20Z 11.59 2521  72  63 -20 0.00
Tue 01/20 21Z 9.82 2622  74  53 -20 0.00
Tue 01/20 22Z 4.19 2623  79  49 -21 0.00
Tue 01/20 23Z 3.97 2624  80  47 -21 0.00
Wed 01/21 00Z 2.85 2626  78  45 -21 0.00
Wed 01/21 01Z 1.95 2628  76  43 -21 0.00
Wed 01/21 02Z 1.51 2628  78  39 -21 0.00
Wed 01/21 03Z 1.27 2628  82  38 -20 0.00
Wed 01/21 04Z 1.10 2627  85  39 -20 0.00
Wed 01/21 05Z 1.00 2627  86  38 -20 0.00
Wed 01/21 06Z 0.91 2627  86  35 -19 0.00
Wed 01/21 07Z 0.78 2626  83  32 -19 0.00
Wed 01/21 08Z 0.82 2528  83  25 -19 0.00
Wed 01/21 09Z 0.73 2527  78  14 -18 0.00
Wed 01/21 10Z 0.64 2526  70  12 -17 0.00
Wed 01/21 11Z 0.64 2527  62  10 -16 0.00
Wed 01/21 12Z 0.64 2528  61  10 -16 0.00
Wed 01/21 13Z 0.61 2527  59  15 -15 0.00
Wed 01/21 14Z 0.56 2526  54  16 -15 0.00
Wed 01/21 15Z 0.50 2423  50  36 -14 0.00
Wed 01/21 16Z 0.47 2323  46  80 -14 0.00
Wed 01/21 17Z 0.43 2223  34  93 -14 0.00
Wed 01/21 18Z 0.40 2024  31  95 -13 0.00
Wed 01/21 19Z 0.44 2025  36  90 -13 0.00
Wed 01/21 20Z 0.37 1926  47  91 -12 0.00
Wed 01/21 21Z 0.31 1928  70  88 -11 0.00
Wed 01/21 22Z 0.32 1935  88  91 -10 0.03
Wed 01/21 23Z 0.52 2041  92  92 -11 0.04
Thu 01/22 00Z 0.61 2043  93  89 -10 0.02
Thu 01/22 01Z 0.69 2143  94  89 -10 0.02
Thu 01/22 02Z 0.77 2141  95  91  -9 0.02
Thu 01/22 03Z 0.82 2140  96  90  -9 0.02
Thu 01/22 04Z 0.78 2238  95  83  -8 0.01
Thu 01/22 05Z 0.76 2237  93  66  -8 0.01

Run total areal avg QPF for the Central_Greens is: 0.19 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