NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260916_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 09/16 06Z 0.46 2420  72  81  12 0.00
Wed 09/16 07Z 0.52 2522  77  84  12 0.00
Wed 09/16 08Z 0.46 2619  85  99  12 0.01
Wed 09/16 09Z 0.39 2616  88  93  12 0.01
Wed 09/16 10Z 0.37 2615  89  83  13 0.00
Wed 09/16 11Z 0.35 2614  90  86  13 0.00
Wed 09/16 12Z 0.33 2613  92  78  13 0.00
Wed 09/16 13Z 0.35 2714  92  73  13 0.00
Wed 09/16 14Z 0.35 2714  93  71  13 0.00
Wed 09/16 15Z 0.34 2713  94  82  14 0.00
Wed 09/16 16Z 0.32 2812  94  86  14 0.00
Wed 09/16 17Z 0.32 2812  97  86  13 0.00
Wed 09/16 18Z 0.27 2910  96  63  14 0.00
Wed 09/16 19Z 0.25 2909  95  51  14 0.00
Wed 09/16 20Z 0.26 2909  97  25  13 0.00
Wed 09/16 21Z 0.22 3008  97  12  13 0.00
Wed 09/16 22Z 0.20 3008  97   8  13 0.00
Wed 09/16 23Z 0.18 3008  97   8  13 0.00
Thu 09/17 00Z 0.16 3108  96   8  13 0.00
Thu 09/17 01Z 0.12 3106  95   9  13 0.00
Thu 09/17 02Z 0.10 3005  94  12  13 0.01
Thu 09/17 03Z 0.12 2905  93  17  12 0.00
Thu 09/17 04Z 0.13 2905  93  24  12 0.00
Thu 09/17 05Z 0.14 2805  89  34  12 0.00
Thu 09/17 06Z 0.15 2805  91  35  12 0.00
Thu 09/17 07Z 0.14 2605  90  34  12 0.00
Thu 09/17 08Z 0.15 2505  90  36  12 0.00
Thu 09/17 09Z 0.16 2506  88  38  12 0.00
Thu 09/17 10Z 0.15 2306  87  39  13 0.00
Thu 09/17 11Z 0.16 2306  87  43  12 0.00
Thu 09/17 12Z 0.18 2307  90  55  12 0.00
Thu 09/17 13Z 0.17 2306  90  61  12 0.00
Thu 09/17 14Z 0.17 2307  90  66  12 0.00
Thu 09/17 15Z 0.17 2207  88  76  12 0.00
Thu 09/17 16Z 0.19 2208  84  84  13 0.00
Thu 09/17 17Z 0.23 2310  80  87  13 0.00
Thu 09/17 18Z 0.26 2410  81  86  13 0.00
Thu 09/17 19Z 0.29 2410  85  87  13 0.00
Thu 09/17 20Z 0.29 2510  87  88  13 0.01
Thu 09/17 21Z 0.26 2508  85  87  13 0.01
Thu 09/17 22Z 0.27 2508  87  95  12 0.02
Thu 09/17 23Z 0.22 2507  86  94  13 0.02
Fri 09/18 00Z 0.18 2506  82  90  13 0.01
Fri 09/18 01Z 0.18 2506  82  87  13 0.01
Fri 09/18 02Z 0.17 2506  83  66  13 0.01
Fri 09/18 03Z 0.17 2606  85  52  13 0.01
Fri 09/18 04Z 0.16 2806  86  32  13 0.00
Fri 09/18 05Z 0.15 2907  85  38  13 0.00
Fri 09/18 06Z 0.17 3009  78  52  13 0.00
Fri 09/18 07Z 0.18 3113  67  72  13 0.00
Fri 09/18 08Z 0.18 3216  58  86  12 0.00
Fri 09/18 09Z 0.18 3219  50  82  12 0.01
Fri 09/18 10Z 0.22 3222  47  77  11 0.00
Fri 09/18 11Z 0.23 3224  55  60  10 0.00
Fri 09/18 12Z 0.25 3224  61  33   9 0.00
Fri 09/18 13Z 0.26 3225  75  30   8 0.00
Fri 09/18 14Z 0.32 3226  79  18   7 0.00
Fri 09/18 15Z 0.40 3225  82  12   6 0.00
Fri 09/18 16Z 0.81 3225  90   7   5 0.00
Fri 09/18 17Z 0.75 3225  81   2   5 0.00

Run total areal avg QPF for the Central_Greens is: 0.14 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