Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20251208_0000
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 12/08 00Z 0.76 2224  93  83  -8 0.00
Mon 12/08 01Z 1.02 2327  94  88  -9 0.01
Mon 12/08 02Z 1.07 2427  95  86  -9 0.02
Mon 12/08 03Z 0.93 2625  95  89  -9 0.03
Mon 12/08 04Z 0.67 2924  94  76 -11 0.02
Mon 12/08 05Z 0.50 3025  92  56 -13 0.01
Mon 12/08 06Z 0.48 3127  93  31 -15 0.00
Mon 12/08 07Z 0.55 3127  93  23 -16 0.00
Mon 12/08 08Z 0.65 3127  93  11 -17 0.00
Mon 12/08 09Z 0.76 3127  92   5 -18 0.00
Mon 12/08 10Z 1.16 3128  90   7 -19 0.00
Mon 12/08 11Z 1.74 3129  90   7 -20 0.01
Mon 12/08 12Z 1.99 3129  85   6 -21 0.00
Mon 12/08 13Z 0.49 3230  71   6 -20 0.00
Mon 12/08 14Z 0.20 3329  59   6 -18 0.00
Mon 12/08 15Z 0.11 3427  54   5 -18 0.00
Mon 12/08 16Z 0.13 3323  49   5 -18 0.00
Mon 12/08 17Z 0.18 3321  45   6 -18 0.00
Mon 12/08 18Z 0.23 3220  43   6 -18 0.00
Mon 12/08 19Z 0.26 3220  41   6 -17 0.00
Mon 12/08 20Z 0.31 3119  40   7 -17 0.00
Mon 12/08 21Z 0.34 3118  38   9 -17 0.00
Mon 12/08 22Z 0.39 3017  35  11 -17 0.00
Mon 12/08 23Z 0.40 3017  33  15 -17 0.00
Tue 12/09 00Z 0.39 3016  30  18 -16 0.00
Tue 12/09 01Z 0.36 3016  28  22 -16 0.00
Tue 12/09 02Z 0.34 2915  28  24 -16 0.00
Tue 12/09 03Z 0.33 2915  27  29 -15 0.00
Tue 12/09 04Z 0.32 2814  26  34 -15 0.00
Tue 12/09 05Z 0.32 2814  24  39 -15 0.00
Tue 12/09 06Z 0.31 2814  22  46 -14 0.00
Tue 12/09 07Z 0.30 2814  22  49 -14 0.00
Tue 12/09 08Z 0.30 2814  24  48 -14 0.00
Tue 12/09 09Z 0.30 2814  24  48 -13 0.00
Tue 12/09 10Z 0.29 2814  23  44 -13 0.00
Tue 12/09 11Z 0.26 2813  23  40 -13 0.00
Tue 12/09 12Z 0.25 2711  24  36 -13 0.00
Tue 12/09 13Z 0.24 2510  24  20 -13 0.00
Tue 12/09 14Z 0.24 2311  23  14 -12 0.00
Tue 12/09 15Z 0.27 2214  24  13 -12 0.00
Tue 12/09 16Z 0.31 2117  26  12 -12 0.00
Tue 12/09 17Z 0.37 2219  30  13 -12 0.00
Tue 12/09 18Z 0.40 2120  28  11 -12 0.00
Tue 12/09 19Z 0.42 2121  24  13 -12 0.00
Tue 12/09 20Z 0.41 2021  21  53 -11 0.00
Tue 12/09 21Z 0.39 2023  20  77 -11 0.00
Tue 12/09 22Z 0.46 2025  24  84 -11 0.00
Tue 12/09 23Z 0.49 2026  34  85 -11 0.00
Wed 12/10 00Z 0.56 2128  54  89 -11 0.00
Wed 12/10 01Z 0.59 2130  85  90 -11 0.00
Wed 12/10 02Z 0.68 2232  94  94 -11 0.01
Wed 12/10 03Z 0.72 2232  95  91 -11 0.01
Wed 12/10 04Z 0.71 2231  95  81 -10 0.01
Wed 12/10 05Z 0.66 2228  96  71  -9 0.01
Wed 12/10 06Z 0.65 2227  96  83  -9 0.01
Wed 12/10 07Z 0.57 2225  95  78  -8 0.02
Wed 12/10 08Z 0.49 2222  96  71  -7 0.01
Wed 12/10 09Z 0.40 2120  96  85  -7 0.01
Wed 12/10 10Z 0.38 2120  95  89  -7 0.01
Wed 12/10 11Z 0.31 2019  95  90  -6 0.02

Run total areal avg QPF for the Central_Greens is: 0.22 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