NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260913_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)
=== ===== === ==== ==== === === === ====
Sun 09/13 00Z 0.38 2016  85   8  11 0.00
Sun 09/13 01Z 0.48 2020  84  15  11 0.00
Sun 09/13 02Z 0.57 2123  85  28  12 0.00
Sun 09/13 03Z 0.56 2123  87  38  12 0.00
Sun 09/13 04Z 0.54 2223  91  55  13 0.00
Sun 09/13 05Z 0.52 2225  95  82  13 0.01
Sun 09/13 06Z 0.54 2227  96  78  14 0.04
Sun 09/13 07Z 0.56 2229  96  92  14 0.08
Sun 09/13 08Z 0.57 2229  97  94  14 0.15
Sun 09/13 09Z 0.57 2328  97  92  14 0.18
Sun 09/13 10Z 0.61 2329  97  94  14 0.11
Sun 09/13 11Z 0.57 2426  97  92  14 0.08
Sun 09/13 12Z 0.56 2326  97  91  14 0.07
Sun 09/13 13Z 0.55 2324  97  93  14 0.07
Sun 09/13 14Z 0.48 2320  97  91  14 0.06
Sun 09/13 15Z 0.45 2319  98  93  14 0.06
Sun 09/13 16Z 0.46 2318  98  87  14 0.05
Sun 09/13 17Z 0.38 2315  97  53  14 0.01
Sun 09/13 18Z 0.29 2311  94  36  15 0.00
Sun 09/13 19Z 0.29 2409  93  37  15 0.00
Sun 09/13 20Z 0.37 2511  92  56  14 0.00
Sun 09/13 21Z 0.39 2512  88  36  15 0.00
Sun 09/13 22Z 0.46 2615  89  41  15 0.00
Sun 09/13 23Z 0.54 2617  91  48  15 0.00
Mon 09/14 00Z 0.65 2620  92  55  14 0.01
Mon 09/14 01Z 0.71 2621  91  56  14 0.02
Mon 09/14 02Z 0.83 2623  93  61  14 0.02
Mon 09/14 03Z 0.63 2720  85  63  14 0.01
Mon 09/14 04Z 0.64 2821  79  60  13 0.00
Mon 09/14 05Z 0.70 2923  79  66  12 0.00
Mon 09/14 06Z 0.53 3023  76  81  11 0.00
Mon 09/14 07Z 0.53 3021  70  92  10 0.01
Mon 09/14 08Z 0.60 2920  82  86   8 0.02
Mon 09/14 09Z 0.59 3021  89  77   7 0.02
Mon 09/14 10Z 0.62 3022  94  39   7 0.01
Mon 09/14 11Z 0.56 3023  93  18   6 0.01
Mon 09/14 12Z 0.44 3123  88   9   6 0.01
Mon 09/14 13Z 0.35 3225  83   7   5 0.00
Mon 09/14 15Z 0.22 3323  79   5   6 0.00
Mon 09/14 16Z 0.18 3321  78   7   6 0.00
Mon 09/14 17Z 0.20 3319  79   8   5 0.00
Mon 09/14 18Z 0.27 3317  79   7   5 0.00
Mon 09/14 19Z 0.29 3317  77   7   5 0.00
Mon 09/14 20Z 0.22 3317  77   6   5 0.00
Mon 09/14 21Z 0.16 3317  73   9   5 0.00
Mon 09/14 22Z 0.13 3318  73  13   5 0.00
Mon 09/14 23Z 0.11 3420  72  16   5 0.00
Tue 09/15 00Z 0.09 3421  71  16   5 0.00
Tue 09/15 01Z 0.05 3421  68  15   5 0.00
Tue 09/15 02Z 0.02 3420  65  14   6 0.00
Tue 09/15 03Z 0.04 3519  61  13   7 0.00
Tue 09/15 04Z 0.06 3517  58  13   8 0.00
Tue 09/15 05Z 0.09 0015  53  11   8 0.00
Tue 09/15 06Z 0.14 0212  47   8   9 0.00
Tue 09/15 07Z 0.12 0211  47   8   9 0.00
Tue 09/15 08Z 0.12 0210  46   7   8 0.00
Tue 09/15 09Z 0.14 0308  47   6   8 0.00
Tue 09/15 10Z 0.15 0606  44   5   8 0.00
Tue 09/15 11Z 0.15 0706  43   4   8 0.00

Run total areal avg QPF for the Central_Greens is: 1.11 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