Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260125_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 01/25 06Z 0.14 3113  50  13 -18 0.00
Sun 01/25 07Z 0.13 3113  49  11 -17 0.00
Sun 01/25 08Z 0.13 3111  48  11 -17 0.00
Sun 01/25 09Z 0.13 3010  48  10 -16 0.00
Sun 01/25 10Z 0.10 3109  47  13 -16 0.00
Sun 01/25 11Z 0.06 3106  45  16 -16 0.00
Sun 01/25 12Z 0.04 2802  43  32 -15 0.00
Sun 01/25 14Z 0.01 1704  39  80 -15 0.00
Sun 01/25 15Z 0.01 1707  48  87 -16 0.00
Sun 01/25 16Z 0.06 1407  68  87 -16 0.00
Sun 01/25 17Z 0.08 1308  83  87 -16 0.00
Sun 01/25 18Z 0.13 1312  85  87 -15 0.01
Sun 01/25 19Z 0.16 1317  85  88 -15 0.03
Sun 01/25 20Z 0.16 1420  85  89 -15 0.04
Sun 01/25 21Z 0.18 1421  86  90 -14 0.06
Sun 01/25 22Z 0.21 1424  86  91 -14 0.07
Sun 01/25 23Z 0.28 1328  86  91 -14 0.08
Mon 01/26 00Z 0.33 1331  86  91 -13 0.09
Mon 01/26 01Z 0.37 1231  85  94 -13 0.06
Mon 01/26 02Z 0.40 1130  86  96 -12 0.05
Mon 01/26 03Z 0.41 1129  86  91 -12 0.04
Mon 01/26 04Z 0.41 1026  86  91 -12 0.05
Mon 01/26 05Z 0.47 1026  86  91 -13 0.05
Mon 01/26 06Z 0.54 1028  86  90 -13 0.06
Mon 01/26 07Z 0.54 1027  86  91 -13 0.04
Mon 01/26 08Z 0.53 0927  87  93 -13 0.02
Mon 01/26 09Z 0.50 1025  87  92 -13 0.01
Mon 01/26 10Z 0.46 1023  87  91 -13 0.01
Mon 01/26 11Z 0.42 1022  87  88 -13 0.01
Mon 01/26 12Z 0.39 1021  87  90 -13 0.01
Mon 01/26 13Z 0.34 1118  86  89 -12 0.00
Mon 01/26 14Z 0.30 1116  87  91 -12 0.00
Mon 01/26 15Z 0.27 1115  88  91 -12 0.00
Mon 01/26 16Z 0.25 1213  89  92 -12 0.00
Mon 01/26 17Z 0.23 1311  89  89 -12 0.00
Mon 01/26 18Z 0.20 1310  90  85 -12 0.01
Mon 01/26 19Z 0.19 1309  91  87 -12 0.01
Mon 01/26 20Z 0.14 1408  92  90 -13 0.02
Mon 01/26 21Z 0.07 1806  92  92 -13 0.01
Mon 01/26 22Z 0.29 2309  90  90 -13 0.02
Mon 01/26 23Z 0.45 2513  89  82 -14 0.03
Tue 01/27 00Z 0.61 2615  89  82 -15 0.03
Tue 01/27 01Z 0.84 2919  90  84 -17 0.02
Tue 01/27 02Z 0.61 3021  90  82 -17 0.01
Tue 01/27 03Z 0.49 3121  90  78 -18 0.01
Tue 01/27 04Z 0.51 3122  91  76 -19 0.01
Tue 01/27 05Z 0.48 3124  91  72 -19 0.01
Tue 01/27 06Z 0.50 3126  90  65 -19 0.00
Tue 01/27 07Z 0.50 3128  90  58 -19 0.00
Tue 01/27 08Z 0.53 3028  88  53 -19 0.00
Tue 01/27 09Z 0.53 3028  86  47 -19 0.00
Tue 01/27 10Z 0.53 3028  79  43 -19 0.00
Tue 01/27 11Z 0.50 3027  68  32 -19 0.00
Tue 01/27 12Z 0.47 3027  66  20 -19 0.00
Tue 01/27 13Z 0.46 3026  72  30 -18 0.00
Tue 01/27 14Z 0.42 3022  75  30 -18 0.00
Tue 01/27 15Z 0.41 2917  81  28 -18 0.00
Tue 01/27 16Z 0.41 2712  83  68 -18 0.00
Tue 01/27 17Z 0.39 2509  81  83 -18 0.00

Run total areal avg QPF for the Central_Greens is: 0.98 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