NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260409_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)
=== ===== === ==== ==== === === === ====
Thu 04/09 00Z 0.23 2108  39   5  -2 0.00
Thu 04/09 01Z 0.24 2110  32  13  -1 0.00
Thu 04/09 02Z 0.28 2113  27  20  -1 0.00
Thu 04/09 03Z 0.32 2115  24  25   0 0.00
Thu 04/09 04Z 0.38 2117  26  30   0 0.00
Thu 04/09 05Z 0.40 2219  26  36   0 0.00
Thu 04/09 06Z 0.38 2220  24  39   1 0.00
Thu 04/09 07Z 0.34 2220  23  39   2 0.00
Thu 04/09 08Z 0.34 2220  23  39   2 0.00
Thu 04/09 09Z 0.32 2121  21  39   3 0.00
Thu 04/09 10Z 0.31 2121  18  39   3 0.00
Thu 04/09 11Z 0.32 2122  17  39   3 0.00
Thu 04/09 12Z 0.30 2121  15  42   3 0.00
Thu 04/09 13Z 0.31 2122  15  46   3 0.00
Thu 04/09 14Z 0.33 2123  16  50   3 0.00
Thu 04/09 15Z 0.34 2024  17  57   3 0.00
Thu 04/09 16Z 0.36 2024  18  69   3 0.00
Thu 04/09 17Z 0.40 2024  19  68   3 0.00
Thu 04/09 18Z 0.48 2025  20  49   3 0.00
Thu 04/09 19Z 0.61 2026  20  18   3 0.00
Thu 04/09 20Z 0.51 2027  19  37   4 0.00
Thu 04/09 21Z 0.49 2027  20  42   5 0.00
Thu 04/09 22Z 0.44 2027  24  49   6 0.00
Thu 04/09 23Z 0.43 2128  28  52   6 0.00
Fri 04/10 00Z 0.46 2129  33  54   7 0.00
Fri 04/10 01Z 0.52 2229  39  58   6 0.00
Fri 04/10 02Z 0.54 2329  46  69   6 0.00
Fri 04/10 03Z 0.55 2329  52  78   6 0.00
Fri 04/10 04Z 0.60 2431  56  68   6 0.00
Fri 04/10 05Z 0.63 2430  62  63   6 0.00
Fri 04/10 06Z 0.61 2429  65  51   5 0.00
Fri 04/10 07Z 0.60 2428  67  66   5 0.00
Fri 04/10 08Z 0.59 2526  72  78   5 0.00
Fri 04/10 09Z 0.55 2425  83  74   5 0.00
Fri 04/10 10Z 0.53 2524  84  61   5 0.00
Fri 04/10 11Z 0.53 2524  76  31   6 0.00
Fri 04/10 12Z 0.52 2523  78  38   6 0.00
Fri 04/10 13Z 0.52 2424  83  82   6 0.00
Fri 04/10 14Z 0.53 2324  84  88   7 0.00
Fri 04/10 15Z 0.62 2328  89  93   6 0.01
Fri 04/10 16Z 0.67 2429  85  89   7 0.01
Fri 04/10 17Z 0.78 2327  81  44   7 0.00
Fri 04/10 18Z 0.96 2327  75  29   7 0.00
Fri 04/10 19Z 1.24 2327  66  48   8 0.00
Fri 04/10 20Z 1.60 2227  63  43   8 0.00
Fri 04/10 21Z 1.83 2228  66  43   8 0.00
Fri 04/10 22Z 1.21 2128  69  63   8 0.00
Fri 04/10 23Z 1.10 2231  77  94   8 0.01
Sat 04/11 00Z 1.04 2430  89  96   6 0.11
Sat 04/11 01Z 0.72 2526  97  97   6 0.09
Sat 04/11 02Z 0.55 2622  98  93   5 0.10
Sat 04/11 03Z 0.40 2819  98  96   4 0.06
Sat 04/11 04Z 0.30 2917  98  91   2 0.04
Sat 04/11 05Z 0.29 3019  97  87   0 0.03
Sat 04/11 06Z 0.32 3121  96  65   0 0.01
Sat 04/11 07Z 0.32 3123  94  42  -2 0.00
Sat 04/11 08Z 0.39 3125  94   9  -4 0.01
Sat 04/11 09Z 0.43 3126  94  10  -5 0.01
Sat 04/11 10Z 0.43 3126  90  10  -5 0.01
Sat 04/11 11Z 0.39 3127  84  11  -5 0.01

Run total areal avg QPF for the Central_Greens is: 0.51 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