NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260930_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)
=== ===== === ==== ==== === === === ====
Wed 09/30 00Z 0.05 0008  96  76   9 0.00
Wed 09/30 01Z 0.05 0008  95  75  10 0.00
Wed 09/30 02Z 0.05 0007  95  70  10 0.00
Wed 09/30 03Z 0.06 0106  95  67  10 0.00
Wed 09/30 04Z 0.03 0005  95  64  10 0.00
Wed 09/30 05Z 0.01 3504  94  60  10 0.00
Wed 09/30 06Z 0.02 3403  93  55  10 0.00
Wed 09/30 07Z 0.04 3102  93  51  10 0.00
Wed 09/30 08Z 0.07 2903  93  45  10 0.00
Wed 09/30 09Z 0.09 3005  94  40   9 0.00
Wed 09/30 10Z 0.08 3005  92  37   9 0.00
Wed 09/30 11Z 0.07 3105  91  34  10 0.00
Wed 09/30 12Z 0.07 3104  91  32  10 0.00
Wed 09/30 13Z 0.07 3004  90  32  10 0.00
Wed 09/30 14Z 0.04 2702  87  31  11 0.00
Wed 09/30 15Z 0.06 2402  87  30  11 0.00
Wed 09/30 16Z 0.08 2304  86  32  11 0.00
Wed 09/30 17Z 0.11 2305  87  32  11 0.00
Wed 09/30 18Z 0.12 2405  86  25  11 0.00
Wed 09/30 19Z 0.14 2406  83  19  12 0.00
Wed 09/30 20Z 0.16 2507  78  19  12 0.00
Wed 09/30 21Z 0.16 2607  70  18  12 0.00
Wed 09/30 22Z 0.18 2607  66  16  12 0.00
Wed 09/30 23Z 0.25 2711  66  17  12 0.00
Thu 10/01 00Z 0.26 2811  74  17  12 0.00
Thu 10/01 01Z 0.29 2712  81  22  12 0.00
Thu 10/01 02Z 0.31 2713  77  28  12 0.00
Thu 10/01 03Z 0.35 2714  69  28  12 0.00
Thu 10/01 04Z 0.35 2714  68  19  12 0.00
Thu 10/01 05Z 0.34 2713  72  21  12 0.00
Thu 10/01 06Z 0.39 2714  75  39  12 0.00
Thu 10/01 07Z 0.41 2714  77  46  12 0.00
Thu 10/01 08Z 0.40 2614  79  62  12 0.00
Thu 10/01 09Z 0.54 2616  90  57  11 0.00
Thu 10/01 10Z 0.47 2515  83  56  11 0.00
Thu 10/01 11Z 0.46 2415  82  40  11 0.00
Thu 10/01 12Z 0.47 2416  81  54  11 0.00
Thu 10/01 13Z 0.52 2417  87  47  11 0.00
Thu 10/01 14Z 0.50 2317  85  59  11 0.00
Thu 10/01 15Z 0.59 2319  93  81  10 0.01
Thu 10/01 16Z 0.60 2319  92  89  10 0.01
Thu 10/01 17Z 0.66 2321  87  91  10 0.00
Thu 10/01 18Z 0.72 2323  90  97  11 0.00
Thu 10/01 19Z 0.67 2425  96  97  12 0.02
Thu 10/01 20Z 0.76 2429  96  96  12 0.07
Thu 10/01 21Z 0.78 2533  95  85  14 0.03
Thu 10/01 22Z 0.80 2533  93  87  14 0.01
Thu 10/01 23Z 0.79 2532  92  83  14 0.01
Fri 10/02 00Z 0.87 2434  92  62  14 0.01
Fri 10/02 01Z 0.97 2436  91  57  14 0.01
Fri 10/02 02Z 1.05 2438  86  71  14 0.02
Fri 10/02 03Z 1.09 2440  85  84  15 0.01
Fri 10/02 04Z 1.17 2441  85  91  14 0.01
Fri 10/02 05Z 1.30 2440  89  93  13 0.02
Fri 10/02 06Z 1.22 2537  92  93  13 0.02
Fri 10/02 07Z 1.11 2534  94  91  13 0.04
Fri 10/02 08Z 0.98 2531  96  96  13 0.07
Fri 10/02 09Z 0.83 2627  97  98  13 0.11
Fri 10/02 10Z 0.69 2622  98  97  13 0.13
Fri 10/02 11Z 0.52 2717  98  95  12 0.11

Run total areal avg QPF for the Central_Greens is: 0.72 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