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SCIENCE · INVESTIGATE AND EXPLAIN

Audit a recorded time series

Decode actual archived station values, irregular times and missing pressure.

Learning outcome: Preserve UTC, field scales and meteorological wind conventions in endpoint comparisons.

Starting recap

The selected FM-16 report is seven minutes after 22:53 and lacks pressure; no relative humidity is calculated.

All lessons are open directly. Your saved experiments remain when you leave and return.

Try

Records 18:53 to 20:53 differ by 120 minutes, +1.1 degrees C temperature and -3.5 hPa pressure.

Open the experiment

Predict

What changes if the special observation is placed at an equally spaced index?

Experiment

Decode a raw row, compare early endpoints and inspect the missing-pressure record and UTC date rollover.

Compare a recorded weather sequence

Historical NOAA station sequence · Ten fixed NOAA/NCEI observations from Denver on December21–22,2022. All times are UTC, and differences are B minus A. Selection never changes observations. Missing pressure stays unavailable, even for the same missing record. Sea-level pressure is a reference-level reduction. Wind bearing is FROM, not direction of travel. Endpoint changes are not forecasts, continuous trajectories, spatial pressure gradients or an automatic front detector.

Reset keeps your prediction, captures and practice history.

Ten observations, one airport, eight hours

Denver International Airport, December 21–22, 2022. Select endpoints to compare reported weather; every point stays fixed. Times below are UTC. The special 23:00 report is only seven minutes after 22:53. Horizontal positions represent elapsed time, not record number.

Forward time order: B follows A. Signed elapsed time B − A: 60 minutes. Endpoint changes are not rates or predictions.

B minus A; missing evidence is not zero
QuantityDifference
Temperature-20.6 °C
Dew point-6.7 °C
Sea-level pressure+7.5 hPa
Wind speed+1.1 m/s
Shortest FROM-bearing change+10.0 °

Wind bearings name where wind comes FROM, clockwise from true north. The shortest signed bearing difference lies from −180° inclusive to +180° exclusive; opposite bearings use −180°. This endpoint difference does not show which continuous turn the wind actually followed.

Temperature / dew point (°C)-30-15015AB012345678Hours after December 21, 18:53 UTCSolid: temperature; dashed: dew point.
Sea-level pressure (hPa), nonzero baseline1000101010201030AB012345678Hours after December 21, 18:53 UTC23:00 pressure is missing: no line bridges the gap.
Wind speed (m/s)0481216AB012345678Hours after December 21, 18:53 UTCConnecting lines guide the eye; intermediate values are not observations.

All panels keep the same horizontal spacing. Lines guide the eye between reported points; they do not create intermediate measurements. Pressure is reduced to sea level, not the airport’s station pressure. Its fixed 1000–1030 hPa scale does not start at zero. A pressure change over time at one location is not a spatial pressure gradient.

Selected NOAA reports; UTC timestamps, routine METAR or special SPECI
Endpoint / UTCTypeTemperature °CDew point °CSea-level hPaWind FROM °Speed m/s
2022-12-21 18:53:00 UTCRoutine METAR8.9-14.41007.31801.5
2022-12-21 19:53:00 UTCRoutine METAR10.0-13.91005.92808.2
2022-12-21 20:53:00 UTCRoutine METAR10.0-12.21003.82508.8
2022-12-21 21:53:00 UTCRoutine METAR8.3-11.71003.631011.8
A 2022-12-21 22:53:00 UTCRoutine METAR5.6-11.11006.95011.8
2022-12-21 23:00:00 UTCSpecial SPECI-8.3-12.2Missing5014.4
B 2022-12-21 23:53:00 UTCRoutine METAR-15.0-17.81014.46012.9
2022-12-22 00:53:00 UTCRoutine METAR-18.3-21.71020.5307.7
2022-12-22 01:53:00 UTCRoutine METAR-20.0-22.81022.1104.6
2022-12-22 02:53:00 UTCRoutine METAR-21.7-25.01024.2306.2
Inspect source conventions and limits

This is a deliberately selected historical event window, not a random sample, complete archive or climate trend. Temperature, dew point, pressure and speed are decoded from tenths in the source fields. Decimal encoding does not establish measurement accuracy. The pressure sentinel 99999 at 23:00 means missing; its quality flag 9 alone does not mean missing. Quality flag 5 means the value passed all quality-control checks from an NCEI source, not that uncertainty is zero. Wind type N denotes a normal wind-observation type.

NOAA integrated surface database · Exact source query · Official field-format documentation · NWS December 2022 event context.

The NWS report describes a late-December-21 Arctic front and a 37°F one-hour airport temperature drop. Our 22:53–23:53 UTC pair drops 20.6°C, equivalent to 37.08°F of temperature difference. In MST this is 15:53–16:53 December 21. The agency account may use the same airport observations; it is not an independent replication. These ten points alone do not establish the exact crossing time, regional boundary geometry or next hour’s weather.

Pressure differences start an acceleration; rotation changes its direction

Predict on paper: at two locations at the same height, which way does the pressure-gradient force point? Then face east in imagination: which side is your right? These original diagrams distinguish a force from the air's current motion. They are qualitative, not trajectories calculated from the station records.

Same height; different placesHigherpressureLowerpressurePressure-gradient force →A change over time at onestation cannot give this arrow.Northern HemisphereSouthern HemisphereN ↑E →Current motion east →N ↑E →Current motion east →Deflection to motion's right:south for eastward motion.Deflection to motion's left:north for eastward motion.
Check the forces and try a new direction

At equal height the pressure-gradient force points toward lower pressure. The eastward velocity arrow is not a force arrow. In Earth's rotating frame, the horizontal Coriolis deflection is to a moving parcel's right in the Northern Hemisphere and left in the Southern Hemisphere. For eastward motion those are south and north. For northward motion they are east and west. Rotation does not start still air moving; the horizontal Coriolis effect vanishes at the equator.

Near-surface friction slows motion and changes the balance of forces, allowing wind to cross isobars toward lower pressure. Actual wind need not point directly down the pressure gradient. A rising pressure reading at one station gives a temporal tendency, not a map of the pressure gradient.

Unequal heating helps sustain broad circulation

Predict: how can circulation move energy away from low latitudes? Annotate the rising and sinking branches below, then explain why this diagram cannot predict tomorrow's wind at a particular airport.

Idealized latitude cross-section: equator → North Pole0°~30° N~60° N90° NHadleyFerrelPolarTrade windsWesterliesPolar easterliesSurface wind names include east–west motion, which this latitude section cannot show.
Check the circulation interpretation

Unequal absorbed solar heating creates energy contrasts; atmospheric motion helps transport energy. In this simplified mean pattern, air rises near the equator, moves poleward aloft and sinks in broad subtropical regions. Rotation influences the surface trade winds and midlatitude westerlies. The Ferrel circulation is maintained through weather systems and eddies; the three regions are not identical heat engines.

The polar region has broad sinking and equatorward near-surface flow; a rising branch lies near the subpolar region. Southern Hemisphere broad branches have a corresponding latitude pattern, while Coriolis deflection changes side. These are seasonal and zonal averages: land, oceans, seasons and individual weather systems shift and disrupt the pattern. No parcel must travel around every drawn loop.

A front advances across the ground; its advance is not the local wind

Predict: in each cross-section, which air mass is advancing at the surface? Trace where warmer air can be lifted. The schematic boundaries and arrows below are explanatory constructions, not a spatial reconstruction from the Denver time series.

Cold frontWarm frontColder airWarmer airWarmer airColder airLiftingOverrunningCold air and surface boundary advance →Warm air and surface boundary advance →
Check the front evidence and its limits

A cold front has advancing colder air undercutting warmer air. A warm front has advancing warmer air riding over retreating colder air. The arrow beneath each section shows boundary advance across the ground; a weather vane reports the direction from which local air arrives. Those are different quantities. The slopes are not to scale, and clouds or rain are not guaranteed merely by drawing a boundary.

To argue for a passage, compare temperature, dew point, wind and pressure over a stated interval. One cooling value cannot identify a front. A single station series cannot determine boundary slope, regional position or propagation speed. Use neighboring observations and analyzed weather maps to investigate those spatial claims.

Sources: NOAA explanation of wind and forces and NOAA global circulation overview. These original diagrams illustrate mechanisms; the separate recorded-weather panel supplies the observational evidence.

B minus A: 60 minutes, temperature -20.6 °C, dew point -6.7 °C, sea-level pressure 7.5 hPa. B follows A.

weather-fronts-v1; 2022-12-21T22:53:00Z to 2022-12-21T23:53:00Z. Wind speed difference 1.1 m/s; shortest FROM-bearing difference 10°. Source flags are not uncertainty intervals; one station does not determine a regional front geometry or future weather.

Captures preserve endpoints A and B in the fixed historical NOAA sequence. Replay compares the same observations; it supplies neither new measurements nor a weather forecast.

Understand

Audit the record before interpreting the weather

The lab contains ten actual NOAA NCEI observations from Denver International Airport, station 72565003017, during December 21–22, 2022. They are frozen historical records, not a forecast or synthetic weather sequence. Selecting A and B changes a comparison while the complete selected series remains fixed.

The NOAA Integrated Surface Database overview describes the archive. This activity selects routine FM-15 reports from 18:53 UTC through 02:53 UTC, plus the special FM-16 report at 23:00 UTC. It is a deliberately chosen event window, not every available report or a random climate sample. Excluded observations are not asserted to be nonexistent.

Before reading a graph, copy the first and last full timestamps, the station identity and the variable units. UTC dates matter across midnight. The final three records belong to December 22 even though the earlier records are on December 21. A learner’s local timezone must not silently redefine these source times.

Decode one field carefully

The official ISD format documentation defines field scales, missing sentinels and quality flags. For the first selected record, TMP is +0089,5: the temperature value divides by ten to give 8.9 °C, followed by a quality code. DEW −0144,5 similarly gives dew point −14.4 °C.

SLP 10073,5 becomes sea-level pressure 1007.3 hPa. This is pressure reduced to a reference level, not the directly measured local pressure at Denver’s elevated airport. Do not interchange it with station pressure or an altimeter setting merely because all are pressure-related quantities.

WND contains direction, direction-quality, type, speed and speed-quality. The first record’s 180,5,N,0015,5 represents wind from 180 degrees, normal type, at 1.5 m/s. Wind direction is clockwise from true north and names where the wind comes from. A wind from the south moves toward the north in a simple horizontal sketch.

Quality code 5 indicates the documented checks and source category, not a numerical uncertainty interval or perfect accuracy. Displayed tenths reflect encoding and rounding. They do not establish a measurement-error bound of plus or minus one tenth.

Respect irregular timing and missing pressure

The interval from 22:53 to 23:00 is seven minutes, followed by 53 minutes to 23:53. These records cannot be placed at equally spaced times without distorting the change. The actual elapsed-time axis preserves that distinction; connecting segments are visual guides, not additional observations.

At 23:00 the raw pressure sentinel is 99999, so sea-level pressure is unavailable. It is not 9999.9 hPa or zero. The sentinel establishes missingness; the accompanying quality code alone is not a universal missing-data test. The pressure plot has a gap rather than a fabricated reading.

Select A and B both at 23:00. Temperature difference is zero because the same available value is compared with itself. Pressure difference remains unavailable because neither endpoint supplies pressure. Missing minus missing is not a measured zero change.

Calculate an early comparison

Choose A at December 21 18:53 and B at 20:53 UTC. Elapsed time B minus A is 120 minutes. Temperature changes from 8.9 to 10.0 °C, a +1.1 °C difference. Dew point changes from −14.4 to −12.2 °C, a +2.2 °C difference. Sea-level pressure falls from 1007.3 to 1003.8 hPa, a −3.5 hPa difference.

Write the subtraction explicitly, especially for negative temperatures. Reversing the endpoint selection reverses signed elapsed time and differences; it does not reverse the underlying historical sequence. No relative-humidity calculation is performed: the earlier warm-temperature teaching approximation is not applied to these negative values.

Transfer: repair a flawed worksheet

An unfamiliar worksheet replaces missing pressure with zero and draws a wind arrow toward the recorded FROM bearing. Correct both choices and explain why simply making a smooth-looking graph does not repair the source data.

Check the weather-series transfer

Retain missing pressure as unavailable and preserve the graph gap. A FROM bearing names the origin of moving air, so a velocity arrow points toward the opposite bearing. Smooth interpolation or a zero placeholder would invent information; it does not provide the missing observation or correct the directional convention.

Apply

The missing pressure sentinel should become:

Public practice checks a specific claim. It does not establish independent mastery.

Separate quality flags and display precision from uncertainty intervals.

Continue

Completion requires a saved prediction, at least one capture and a reflection. Presence checks do not grade your reasoning.

Skipping retains experiments and awards no mastery.

Previous: Unequal heating and circulation patternsNext: Assemble a multi-variable front argument
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