NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260204_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)
=== ===== === ==== ==== === === === ====
Wed 02/04 06Z 0.67 2617  89  75 -13 0.00
Wed 02/04 07Z 0.68 2718  94  70 -13 0.00
Wed 02/04 08Z 0.54 2915  93  63 -13 0.00
Wed 02/04 09Z 0.37 2912  87  64 -14 0.00
Wed 02/04 10Z 0.30 2911  88  71 -14 0.00
Wed 02/04 11Z 0.34 2912  90  79 -15 0.00
Wed 02/04 12Z 0.42 2812  89  79 -16 0.01
Wed 02/04 13Z 0.35 2812  88  67 -16 0.01
Wed 02/04 14Z 0.27 2911  85  66 -15 0.00
Wed 02/04 16Z 0.18 3213  81  60 -14 0.00
Wed 02/04 17Z 0.24 3114  81  49 -14 0.00
Wed 02/04 18Z 0.32 3115  82  33 -14 0.00
Wed 02/04 19Z 0.35 3115  83  24 -14 0.00
Wed 02/04 20Z 0.38 3115  86  19 -14 0.00
Wed 02/04 21Z 0.38 3015  87  22 -13 0.00
Wed 02/04 22Z 0.33 3015  85  26 -13 0.00
Wed 02/04 23Z 0.29 3116  84  25 -12 0.00
Thu 02/05 00Z 0.31 3117  86  26 -12 0.00
Thu 02/05 01Z 0.29 3118  86  27 -12 0.00
Thu 02/05 02Z 0.28 3118  84  26 -12 0.00
Thu 02/05 03Z 0.27 3117  82  25 -12 0.00
Thu 02/05 04Z 0.26 3016  81  29 -12 0.00
Thu 02/05 05Z 0.27 3016  80  27 -12 0.00
Thu 02/05 06Z 0.29 3017  80  33 -13 0.00
Thu 02/05 07Z 0.29 3017  81  38 -13 0.00
Thu 02/05 08Z 0.28 3016  80  33 -13 0.00
Thu 02/05 09Z 0.29 3016  81  39 -13 0.00
Thu 02/05 10Z 0.32 3017  83  67 -13 0.00
Thu 02/05 11Z 0.33 3020  82  75 -14 0.00
Thu 02/05 12Z 0.31 3020  80  21 -13 0.00
Thu 02/05 13Z 0.26 3119  79   3 -13 0.00
Thu 02/05 14Z 0.23 3118  78   7 -13 0.00
Thu 02/05 15Z 0.20 3117  77   6 -13 0.00
Thu 02/05 16Z 0.19 3115  76   5 -13 0.00
Thu 02/05 17Z 0.17 3214  72   7 -13 0.00
Thu 02/05 18Z 0.16 3212  68   7 -13 0.00
Thu 02/05 19Z 0.14 3211  63   7 -12 0.00
Thu 02/05 20Z 0.11 3211  61   6 -12 0.00
Thu 02/05 21Z 0.10 3211  57   6 -12 0.00
Thu 02/05 22Z 0.08 3311  53   6 -11 0.00
Thu 02/05 23Z 0.06 3310  50   6 -10 0.00
Fri 02/06 00Z 0.04 3309  46   7 -10 0.00
Fri 02/06 01Z 0.03 3308  45   8  -9 0.00
Fri 02/06 02Z 0.03 3305  45  10  -9 0.00
Fri 02/06 03Z 0.04 3003  43  12  -9 0.00
Fri 02/06 04Z 0.05 2803  43  14  -9 0.00
Fri 02/06 05Z 0.06 2703  44  15  -9 0.00
Fri 02/06 06Z 0.07 2503  44  15  -9 0.00
Fri 02/06 07Z 0.08 2404  45  13  -9 0.00
Fri 02/06 08Z 0.10 2305  46  10  -9 0.00
Fri 02/06 09Z 0.09 2205  45   7 -10 0.00
Fri 02/06 10Z 0.08 2106  45   4 -10 0.00
Fri 02/06 11Z 0.08 2106  46  29 -10 0.00
Fri 02/06 12Z 0.08 2007  48  68 -10 0.00
Fri 02/06 13Z 0.08 2008  49  78 -10 0.00
Fri 02/06 14Z 0.12 2009  52  81 -10 0.00
Fri 02/06 15Z 0.13 2010  58  77 -10 0.00
Fri 02/06 16Z 0.13 2010  60  71 -10 0.00
Fri 02/06 17Z 0.16 2010  61  90 -10 0.00

Run total areal avg QPF for the Central_Greens is: 0.02 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