NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260904_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)
=== ===== === ==== ==== === === === ====
Fri 09/04 00Z 0.73 3019  80  42  14 0.00
Fri 09/04 01Z 0.80 3020  82  34  13 0.00
Fri 09/04 02Z 0.76 3020  83  39  13 0.00
Fri 09/04 03Z 0.56 3116  78  41  13 0.00
Fri 09/04 04Z 0.54 3016  76  45  13 0.00
Fri 09/04 05Z 0.47 3015  77  48  13 0.00
Fri 09/04 06Z 0.36 3013  79  46  13 0.00
Fri 09/04 07Z 0.31 3012  84  46  12 0.00
Fri 09/04 08Z 0.33 3012  89  41  12 0.01
Fri 09/04 09Z 0.25 3111  93  38  12 0.01
Fri 09/04 10Z 0.18 3210  94  39  11 0.01
Fri 09/04 11Z 0.12 3310  91  42  11 0.01
Fri 09/04 12Z 0.15 3311  89  47  11 0.00
Fri 09/04 13Z 0.17 3312  83  37  11 0.01
Fri 09/04 14Z 0.20 3212  78  24  11 0.00
Fri 09/04 15Z 0.60 3212  79  22  10 0.00
Fri 09/04 16Z 1.93 3112  81  26  10 0.00
Fri 09/04 17Z 2.39 3112  84  35  11 0.00
Fri 09/04 18Z 1.38 3112  87  47  11 0.01
Fri 09/04 19Z 1.10 3014  88  45  11 0.01
Fri 09/04 20Z 0.71 3114  87  46  11 0.00
Fri 09/04 21Z 0.64 3114  89  42  11 0.00
Fri 09/04 22Z 0.37 3216  89  35  10 0.00
Fri 09/04 23Z 0.35 3216  90  39  10 0.00
Sat 09/05 00Z 0.25 3316  91  38  10 0.00
Sat 09/05 01Z 0.16 3316  92  39  10 0.00
Sat 09/05 02Z 0.17 3316  92  43  10 0.00
Sat 09/05 03Z 0.14 3317  92  45  10 0.01
Sat 09/05 04Z 0.07 3417  92  46  10 0.00
Sat 09/05 05Z 0.04 3417  93  48  10 0.01
Sat 09/05 06Z 0.02 3515  92  48  10 0.00
Sat 09/05 07Z 0.04 3514  91  52  10 0.00
Sat 09/05 08Z 0.05 3514  92  56  10 0.01
Sat 09/05 09Z 0.08 3515  94  57  10 0.01
Sat 09/05 10Z 0.13 0016  96  63   9 0.01
Sat 09/05 11Z 0.20 0017  96  70   9 0.01
Sat 09/05 12Z 0.23 0117  94  72   9 0.00
Sat 09/05 13Z 0.22 0117  93  69   9 0.00
Sat 09/05 14Z 0.23 0116  94  68   9 0.00
Sat 09/05 15Z 0.25 0116  94  66   9 0.00
Sat 09/05 16Z 0.27 0114  95  66   9 0.00
Sat 09/05 17Z 0.26 0112  95  66   8 0.00
Sat 09/05 18Z 0.30 0111  96  65   8 0.00
Sat 09/05 19Z 0.27 0111  97  65   8 0.01
Sat 09/05 20Z 0.27 0111  97  64   9 0.01
Sat 09/05 21Z 0.31 0211  97  65   8 0.02
Sat 09/05 22Z 0.35 0311  96  66   8 0.01
Sat 09/05 23Z 0.32 0311  97  70   9 0.01
Sun 09/06 00Z 0.38 0412  98  75   8 0.03
Sun 09/06 01Z 0.48 0613  98  78   8 0.04
Sun 09/06 02Z 0.56 0715  95  75   7 0.03
Sun 09/06 03Z 0.52 0716  91  77   7 0.01
Sun 09/06 04Z 0.48 0615  90  80   7 0.00
Sun 09/06 05Z 0.46 0714  85  79   7 0.00
Sun 09/06 06Z 0.42 0713  84  74   6 0.00
Sun 09/06 07Z 0.38 0612  85  64   6 0.00
Sun 09/06 08Z 0.31 0510  86  60   6 0.00
Sun 09/06 09Z 0.28 0411  86  54   6 0.00
Sun 09/06 10Z 0.26 0410  86  50   6 0.00
Sun 09/06 11Z 0.27 0311  85  49   6 0.00

Run total areal avg QPF for the Central_Greens is: 0.30 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