NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260716_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 07/16 00Z 0.69 3022  74  53  13 0.00
Thu 07/16 01Z 0.68 3024  74  43  13 0.00
Thu 07/16 02Z 0.69 3026  73  43  13 0.00
Thu 07/16 03Z 0.62 3027  74  38  14 0.00
Thu 07/16 04Z 0.53 3126  75  32  14 0.00
Thu 07/16 05Z 0.45 3124  76  30  13 0.00
Thu 07/16 06Z 0.40 3122  75  36  13 0.00
Thu 07/16 07Z 0.40 3120  75  40  13 0.00
Thu 07/16 08Z 0.43 3020  73  50  13 0.00
Thu 07/16 09Z 0.45 3020  71  54  13 0.00
Thu 07/16 10Z 0.44 3020  69  54  12 0.00
Thu 07/16 11Z 0.42 3019  70  48  12 0.00
Thu 07/16 12Z 0.41 3018  71  47  12 0.00
Thu 07/16 13Z 0.49 2817  70  47  12 0.00
Thu 07/16 14Z 0.67 2719  69  54  12 0.00
Thu 07/16 15Z 1.15 2721  77  76  12 0.00
Thu 07/16 16Z 4.67 2724  80  68  12 0.03
Thu 07/16 17Z 5.42 2825  81  58  12 0.01
Thu 07/16 18Z 6.69 2827  77  62  12 0.02
Thu 07/16 19Z 10.15 2727  71  44  13 0.00
Thu 07/16 20Z 13.02 2928  75  64  12 0.02
Thu 07/16 21Z 4.06 3133  79  84  11 0.13
Thu 07/16 22Z 0.53 3235  80  80  10 0.12
Thu 07/16 23Z 0.61 3230  74  34  10 0.03
Fri 07/17 00Z 0.65 3227  64  31   9 0.00
Fri 07/17 01Z 0.58 3226  57  20   8 0.00
Fri 07/17 02Z 0.60 3227  57   8   8 0.00
Fri 07/17 03Z 0.56 3228  56  28   8 0.00
Fri 07/17 04Z 0.50 3229  58  28   7 0.00
Fri 07/17 05Z 0.46 3228  63  26   7 0.00
Fri 07/17 06Z 0.45 3228  66  21   7 0.00
Fri 07/17 07Z 0.42 3228  65  15   7 0.00
Fri 07/17 08Z 0.42 3229  69  11   7 0.00
Fri 07/17 09Z 0.37 3229  72  10   8 0.00
Fri 07/17 10Z 0.25 3227  71   9   8 0.00
Fri 07/17 11Z 0.19 3324  70  11   8 0.00
Fri 07/17 12Z 0.15 3322  67   9   9 0.00
Fri 07/17 13Z 0.14 3320  65   9   8 0.00
Fri 07/17 14Z 0.14 3316  62  12   9 0.00
Fri 07/17 15Z 0.18 3214  60  16   9 0.00
Fri 07/17 16Z 0.23 3213  55  15   9 0.00
Fri 07/17 17Z 0.28 3213  50  14   9 0.00
Fri 07/17 18Z 0.49 3112  49  16   9 0.00
Fri 07/17 19Z 0.57 3111  50  15   9 0.00
Fri 07/17 20Z 0.65 3110  54  15  10 0.00
Fri 07/17 21Z 0.61 2908  61  13  10 0.00
Fri 07/17 22Z 0.58 2809  65  11  10 0.00
Fri 07/17 23Z 0.54 2710  64   8  10 0.00
Sat 07/18 00Z 0.52 2611  60   6  11 0.00
Sat 07/18 01Z 0.54 2612  57   6  11 0.00
Sat 07/18 02Z 0.53 2512  55   7  11 0.00
Sat 07/18 03Z 0.55 2512  54   7  11 0.00
Sat 07/18 04Z 0.58 2413  54   5  11 0.00
Sat 07/18 05Z 0.58 2414  52   2  11 0.00
Sat 07/18 06Z 0.60 2416  52   3  11 0.00
Sat 07/18 07Z 0.59 2416  46   9  11 0.00
Sat 07/18 08Z 0.64 2517  51  12  11 0.00
Sat 07/18 09Z 0.69 2517  57  15  11 0.00
Sat 07/18 10Z 0.61 2516  61  30  11 0.00
Sat 07/18 11Z 0.52 2415  62  46  12 0.00

Run total areal avg QPF for the Central_Greens is: 0.36 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